FISHERIES AND MARINE SERVICE Translation Series No. 4422

FISHERIES AND MARINE SERVICE
Translation Series No. 4422
The physiology of differentiation and growth
II. Critical periods in the development of salmonids
and their physiological basis
by A.N. Trifonova et al.
Original title: La physiologie de la différenciation et de la croissance
IL Les périodes critiques dans le développement des salmonides et
leur base physiologique
•From:
Acta Zoo1.20: 239-267, 1939
Translated by
Translation Section
Department of Fisheries and the Environment
Department of the Environment
Fisheries and Marine Service
Faci“c Biological Station
Nanaimo, B,C,
3 8 pages typescript
•
S
•
239
THE PHYSIOLOGY OF DIFFERENTIATION AND GROWTH
IL CRITICAL PERIODS IN THE DEVELOPMENT OF SALMONIDS AND THEIR
PHYSIOLOGICAL BASIS
BY
A N TRIFONOVA, M F VERNIDOUBE and N D PHILIPPOV
(Laboratory of Ichthyology of the State University of Leningrad and
of the Institute for biology of Peterhof. Director: Professor K M DERJUGIN).
TABLE OF CONTENTS
239
Introduction and statement of the question.
240
Critical periods in salmon development
246
Acclimation of fish eggs exposed to high temperatures
248
Growth rate in the development of salmon embryos
250
General data on the growth rate of the salmon embryo
Glycolytic processes in the development of salmon .
254
embryos
7. Respiration during embryonic development of the salmon 258
264
8. General conclusions
1,
2.
3.
4.
5.
6.
1.
INTRODUCTION AND STATEMENT OF THE QUESTION
In the development of fish that spawn in the spring, the periods of
growth and differentiation are characterized by different types of metabolism and by differences in the ability of eggs to resist the effect
of harmful factors. During the period of gastrulation and growth of
the tail (caudal bud), the embryo shows an intensive growth rate, a
shift of the Pasteur-Meyerhof equilibrium boward the predominance
of the processes of anaerobic fission and a high resistance to harmful
factors. During the passage to gastrulation (differentiation of the
embryonic layers) and the formation of the axial organs, the PasteurMeyerhof equilibriumellifts in the opposite direction. The role of
anaerobic processes is suppressed in the metabolism of the eggs and
they are damaged by the slightestuiverse action. The
•
240
type of metabolismi and the reaction of the egg to harmful factors therefore
vary depending on thê . _morohcfgenetic Processes-(Trifonova, 1935-1937;
Privolniev, 1935; NikiforOv, 1937).
The relation between morphogenesis and the type of metabolism has
been established only for fish that spawn in the spring (perch, ruffe),
the embryonic development of which differs considerably from that of the salmon.
In the latter, incorporation is rapid, probably because of the smaller
yolk, and the anlage of the embryo forms at the stage of blastopore
closure. It can be seen, then, that in the development of these fish,
the stage of the anlage of the axial organs almost coincides with the
formation of the caudal bud (Chevey, 1925).
In fish that spawn in the spring, blastopore closure modifies the type
of metabolism (respiration becomes more intense, the glycolysis decreases,
the eggs become more sensitive). If the type of metabolism and the morphogenetic
processes show an interrelationship, we have to know whether this change
in metabolism is linked to the formation of axial organs or to blastopore
closure connected with the formation of the caudal bud. The study of
perch development cannot provide an answer to this question, since in the
perch these two processes almost coincide. In the development of the
salmon, on the other hand, embryo formation and blastopore closure are
separated; -- the axial organs form much earlier, and at the moment of
blastopore closure the embryo already has 28 myotomes. The purpose ofthis
study is firs;to determine whether in salmon development there is a
connection between the type of morphogenesis and the type of metabolism,
similar to that observed in fish that spawn in the spring, and second,
to determine whether the change in metabolism that occurs in the perch
at the stsge of blastopore closure occurs in the salmon at the start
of embryo formation (neural keel) or at the blastopore closure stage.
For the purposes of our study we examined the stability of eggs at various
stages of their development, the growth rate, the respiratory rate and
the formation of lactic acid. As the material for our study we chose the
eggs of Salmo salar.
241
2.
CRITICAL PERIODS IN SALMON DEVELOPMENT
In the development of fish that spawn in the spring, there is hypersensitivity not only at the stages of passage to gastrulation and formation
of the axial organs, but also at the start of segmentation. The sensitivity
of this latter period is related neither to the nature of the morphogenetic
processes nor to the type of metabolism (Trifonova, 1935, page 780). An
acute sensitivity at the start of segmentation is observed in many forms
and is probably caused by the fact that at this period the regulatory
mechanisms of the eggs have not yet had time to develop. According to
Hein (1907, 1911), salmon eggs are especially stable at the start of
development. With time their sensitiveness increases to reach its
maximum on the fourteenth day of development, after which it again decreases.
According to Hata (1927), another salmonid, Oncorynchus mason, possesses
in addition to this sensitivity period to daysfourteen and fifteen of
development, another sensitivity period at the start of segmentation.
During the sensitivity developmental periods, the embryo is easily
harmed by a wide variety of factors (Hein, Svietlov) . Trifonova (1935)
and Privolniev (1935), in their studies of fish that spawn in the spring,
used - respectively asphixia and high temperature as harmful factors.
In the present study, the harmful factor for groducing differentiated
sensitivity is also high temperature (19.5-21 C). At some stages this
temperature causes the rapid destruction of the eggs, whereas at other
stages the eggs will remain alive for dozens of hours. For each experiment
we took 25 eggs which we placed in a crystalizer with 300 ml capacity
containing 200 ml of water. During the experiment we always marked the
point at which the first egg died, then in succession the instant of
death of all the other eggs to the last egg. In some experiments, the
eggs were all dead only after 60 to 70 hours. In all, over a period of
two years (1934-1935), we carried out 95 experiments on 5 batches of eggs.
These experiments covered the whole developmental process from the start
of segmentation to hatching. We fixed the eggs and then made total
preparations (boric carmine), after which we compared experimental results
from the same stages (table I and figure 1). These results clearly show
first, that the salmon, unlike the perch (Perca fluviatilis), in full
agreement with the data of Hein, has its stablest stage at the start of
segmentation (death of the first egg in 28.6 hours and of the last in 58.3
hours) . Our results tallied with Hein's also in that the particularly
acute sensitivity began on the same day of development in our experiments
as in his.
1
The figures are the average of all the experiments at that particular
stage. Table I, bottom line.
242 & 243
Table I. Mortality of salmon eggs under the effect of high temperature.
LEGEND (see photocopy next page)
1. Stages
2. Morula of the large cells
3. Morula of the medium cells
4. Morula of the small cells
5. Start of gastrulation
6. Gastrulation at a more advanced stage
7 «. Growth og the forming embryo
8. Blastopore closure
9. Growth of the embryo until eye pigmentation
10. Series of experiments
11. Time till death in hours:
12. Of the first egg
13. Of all eggs
14. Average
15. Average of all series
LA
'0 V
id dcs irufs du saumon
•
(Ce
/ Croissance de
Gastrulation
b
Plus avancée
Cu heures
—-
du
cr
ce tif
6
le tous
les
wufs
33
moyenne
'`- du."-- t
e tous 114
I9
■•■•■•
teuf
IIMY.
enne
35
56
45.5
',5
.•■■■•
13
40
28
20
.5
.1.■■
œufs
46
27
5
47
26
33,5
4
47
25,5
49.3
,
74
37.2
5. 6
52
6
46.6
31
8
34
25
17,5
-
4.)
6.5
--
31
16,5
7
43
45,5
J
2
--
___
___
6
31
18,5
12
46
29
27
80.3
53,6
5
.32,3
t 8,5
12.2
53,7
33
5
47
31.5
5
34
61
40
—
—
18 .4
1 3.7
38
2.4. 8
4
1 2 .S
IS.2
26,5
25
67
46
to.5
4 8 ,5
3
13
84
40
24
50
.-___
t4
___
1'3
_
-• -
--
33
20
56
60
—
--
—
34
73
—
23
58
- --
--
8. 2
4 8 ,7
5
77
41
3
28,5
6
30
18
15,2
6
28
17
21,3
20,6
53,5
37, 1
4
4,
42
—
7 8 .Ç
20
64
45,5
19
34
70
2(
80
33. 2
6
15
64
--
52.7
18
44,2
--
1 3. 6
30
48
125
:0 7 •
37
34.5
6
21. () !
•
63,5
47.7
16,5
i
11
21 .3
6
49
lo
25
42
---
73
8
1 7,3
24
'9
21,3
11
28,6
34,3
29
33
33
8,2
6
51
_.
._
—
--
42
;
46,3
•
f.
1
•
--
•
I
2
67
48
13
5
25,5
10
13.;
18
12
11
22
21
28
17
17
29
.
26
26
7
32
•--
41
8
---
2(45
54
—
10
47 • 5
—
47
:-
15
70
--
34
•
1
25
21
i6
22
1
1
--
to
25
32,5
10
•
21
51
26
30,5
—
—
Io
14
7
t 1.8
t:
16,5
_
16
14,5
I
25.5
22
45
moy1 ,..,1.,
•
,....tlf;
, t:uf 1
- o•
1 5,5
64
1 ,., •
38
27
26
■
mo enne
._
40
j
en 1ieurN
z,ty.I -,F,5".
--- iir -- .ue
13
4
26
25
--
pi
32
4
3
8
55
c.e. Ion:.
le,
ceuf• a uf-;
70
15
13
9
--1-
1 , :. :
39
24
to
wufs
du
53
6
17
oeuf
moy•
enne
■
Il ,l)ept
• ,
. ri ,--enunt
m
D épéri eent
en he.dre-,
114
22,5
15
les
—
18,5
32
5
1 ,,,,
li
t2_
i.du 13
119
de tous
—
26 . 1
t3
7
Dép érisseent
m
en heures
Croiss.anre de rein
b ryon _ius. t ..1':i la pi g
mentat1on des eu N
Ferme:tire du
lastopore
75
--
1
enne
3 2 ,5
—
7
IllOy-
47
25
55
8
les
45
26
25
teuf
de tous tH
20
30
38
1 er
-
20
25
18
ladu
les
ruas
lei
li
en heures
_
-j---.
i
r)y•
l i Dépérissement
H Dép ■ :ris..ement
23
l'embryon en
forma tio n
_
Dépérissement
en heures
243
FFÉRI.\ci.\ -rioN ET LA cw,Iss :\N- c•r_
dc la haute tempera/ un:.
s ,ms
Getstrulation
Début
1)1
1
1
•
F4,3
46,3
23
13
46
-, 6
--
8
7
23.7
13,8
q.5
64
3 ;.7
.1.; l
37
22 ,3
1 3.3
59.0
36 . 1
5,9
3.1.f.: 1
I
32
2S.7 ,
74
4.4
•
42.5
45
53.5
i
i
57
4 0 ,5
57,5
44-5
_
(!);.b. ■ •
47.2
.....
—
—
._
—
19,7
---
---
1
!
,
4
7,7
5
I 40,1 . 23:9
23.91
385
4 1 ,1
242
rf N. 1). l'1111.11)POV
A. N. T1:1110NOVA, M. V.
Tableau T. Dépérissement des (t-tifs titi saumon
s
I()
Morula des
grandes cellules
s
T ÀD E
•
Séries
(p exp é r i ences
Il Dépérissement
en heures
Il Dépérissement
en heures
312.,
-,ALI 1aetolls
1,î WU:"
iz(Ill (IC
.
Moyenne
5- Gastrulation
1) (1u:tassement
• ••
en heures
11 D eperissement
• •
en heures
$12-,
i 1 1-1
(Ill
â1..1 IOUSI
"").).
enrie
Fr
oeuf
les
o..aifs
45
12
—
--
45
—
28,5
—
I" O Y.
cru(
oeufs
enile
33
57
--
,
Début
—
ii
les
wufs
ICS
1
0-1
Morula des
petites cellules
ir'r
und-
19
ler
{
Ill
Morula d es
cellules moyennes
.
ni°).
enne
•_._
--
47
30,5
D t:p t..r ;S 'e l
C11
!pl
(III (IC IOLIS
moy.
les
1 er
olif wufs " ne
I7
12.
6
33
—
—
—
.
14
l'action
23
42
32,5
18
—
--
--
--
—
--
—
---
•
--
38
d 12
35
56
-20 I
45
;
20 I
47
_
--
25
.1 1/3
28
3C1
1 9, 5
—
53
25
I I.
•
—
--
•-
14
leo.urs
• tuer
—
.
cIt
Ir t
Moyenne
•
-
11,5
a.
26. 1
21
38
2 9-5
30
48
-
39
25
—
114
26 I
_
55
--
27 • 8.D.3
40
26
64
70
---.
1
—
_
—
_
"I
14
Moyenne
1V'
.
•
._
.
l
•-
--
28
46
__
_.
-
37
22
50
36
22
-
14
28
2!
23
1
28
,,,
5 e'
--
-•
25
13
11-1
M oyenne
_
1
1
-
-25
72
4 8 ,5
18
39
44
20
28,5
22.5
32
24
24
--
V
Mo ■ enne
15
Moyenne de toutes
les séries . . .
.
28,6
.
.
58,3
.
43.5
-
16
4
41
28 .5
2 4.3 I
_.
_
52
38
13
32
22,5
47
35.5
7
--
-
7
17
I.1
i;
U)
314
21.31
47.7
6
24
61
:i;
42.5 1
_
2 7.7
24 49.5 3 6 .7
--
34
-3
--
19
24
20
.
—
---
--
.
—
25.5
21
--
—
28
30 ,
_
1
1
I
)
-
8 2 15.2
11,8
30,5 .
21,2
20,6 1,
53,5
244
We have determined the stages that correspond to this change in sensitivity. It. is - here that the first anlage of the embryo originates
(stage of neural keel formation; death of the first egg after 7.7 hours
and of the last after 37 hours). But whereas according to Hein's data
sensitivity increases in regular progression, reaches a maximum, and
then decreases with equal regularity, our data suggest that in salmon
developmentP eriods of stability and sensitivity alternate.
The first sensitive period (the least distinct, it is true)
morula stage of medium cells (figure 2).
is the
In the perch, a similar sensitivity period was not, and could not be,
observed, because the whole period of segmentation of this fish shows
very high sensitivity. The relation between this sensitivity period and
the morphogenetic processes is unclear. We can only venture the suggestion
that it probably occurs when the first sexual cells are formed. The
second sensitivity period, which is more distinct, corresponds to the
stage of the passage to gastrulation (figure 3, stage A). Consequently,
in the salmon as in fish that spawn in the spring, the period preceding_
gastrulation (differentiation of the embryonic layers) is characterized by
high sensitivity.
The third sensitivity period is that of the first anlage of the embryo
(figure 3, stage D). The fourth period is the stage preceding blastopore
closure and the formation of the caudal bud.
Figure 1;
The
MORTALITY OF SALMON EGGS EXPOSED TO HIGH TEMPERATURE.
numbers I-IV at the low points of the troughs of the curve
show the critical periods.
*-Morula stage of medium cells; **-Stage of eye pigmentation. The other
stages of development are designated by letters placed on the curve
(A,B,C,D,E,). Stages are shown on figure 3.
LEGEND (see photocopy next page)
1.
2.
3.
4.
hours
all eggs dead
death of first egg
days of development
Figure 2:
A.
B.
Size of the morula cells before the start of the first
critical period;
during the first critical period. For the location of the
first critical P eriod on the mortality curve, see figure 1.
4.
The drawing was made from the ill icroscope. Eyepiece
Objective; 8 mm. Zeiss. Slide of 160 mm.
244
•
A. N. TRIFONOVA, :1\1. F. VERNI DOLME ET N. D. P1•11LIPPOV
/."
heures
Dépérissement complet
lieu la première
Dépérissement du premier oeuf
de l'embryon (stade du
45
42
•
39
36
,
1
■■■ •,
33
ie 1
g
;
30
\ji•
I
1
Il
27
A I
'
I
l
94
%
1
)4-•
`e
21
18
8-C
15
12
9
6
X
3
. .
1
%
e'k *
//
I
\
sensibilité croit successivement et régulièrement, puis,
après avoir atteint son maximum, baisse de la même
manière, selon nos données
il y a dans le développe-
PZ"
.
.
10
dernier au bout de 37 heures). Mais tandis que, selon
les données de' HEIN, la
./
1
'
5
grossissement bordier; (lestruction du premier œuf
au bout de 7,7 heures et du
eià
.
15
20
25
ment du saumon une alternance de périodes stables et
Jours de développement
Fig. 1. Dépérissement des crufs de saumon sous l'action
des hautes températures. Les chiffres (I-1V) aux
points bas de la courbe indiquent les périodes critiques
-correspondantes. * — stade morula des cellules moyennes; ** — stade de la pigmentation des yeux. Les autres
stades de développement sont désignés par des lettres
placées sur la courbe (A, B, C, 1.), E). Les stades sont
représentés sur la figure 3.
.
ébauch:.•
de périodes sensibles.
La première période sensible (le moins nettement
exprimée, il est vrai) est
le stade morula. des cellules
moyennes (fig. 2).
Chez la perche une période sensible analogue n'a pas été constatée et ne pouvait l'être, parce que chez
ce poisson toute la période de segmentation accuse une sensibilité très élevée.
Le rapport entre cette période de sensibilité et les processus morphog-énétiques
est très peu clair. On peut seulement indiquer que c'est probablement alors
qu'a lieu la formation des cellules sexuelles premières. La seconde période de sensibilité, plus
nettement exprimée, correspond au stade du
passage à la gastrulation (fig. 3, stade A). Par
conséquent, chez le saumon, comme chez les
poissons qui frayent au printemps, la période
précédant la gastrulation (différenciation des
Fig. 2. A dimension des cellules
de la morula avant le commencement de la première période
l endant la première
critique;
période critique. Pour la situation de la première période critique sur la courbe de dépérissement, v. la fig. 1. Le dessin a
été exécuté au niveau de la table
objective. Oculaire 4. Objectif
S min. Zeiss. Tube 16o min.
couches embryonnaires) . se caractérise par une
haute sensibilité.
La troisième période de sensibilité est celle
de la première ébauche de l'en ii
(fig.
3.
stade D).
La quatrième période est le stade gui précède
la fermeture du blastopore et la formation du bourgeon caudal. Comme nous l'avons déjà dit, chez
o.
245
See photocopy next page.
Figure 3.
Schematic depiction
of salmon embryo development.
A. Start of gastrulation (blastodisk still convex); this stage comes in
the second critical period. B, Gastrulation (flattened blastodisk).
C. More advanced stage of gastrulation (the embryonic field is taking
shape but the axial organs are not yet visible). D. Neural keel formation
(Randknopf), the first appearance of the axial organs; this comes in the
third critical period. E. The fully formed embryo lengthens. The
yolk is incorporated by the blastodisk. F. Stage of blastopore closure;
this comes in the fourth critical period.
As we have already said, in the perch, a more rapid development
means that the anlage of the embryo occurs at the stage of blastopore
closure. To this sensitivity period in the development of the perch
there correspond two sensitivity periods in the development of the salmon.
Consequently, the processes of the formation of the axial organs and
blastopore closure are both linked to changes in the stability of the eggs.
The following lists permit comparison of the sensitivity periods of
salmon and fish that spawn in the spring.
Sensitivity periods in fish development.
Salmon
1.
2.
1
3
•2
3.
4.
Morula of average cells
Commencement of gastrulation.
Stage of neural keel formation (amlage of the embryo)
Stage of blastopore closure - (anlage of caudal bud)
Period preceding hatching.
2.15
LA DIFFÉRENCIATION 171' LA CROISSANCE
Fig. 3. Développement schématique de l'embryon du saumon. A commencement de la
gastrulation (blastodisque encore convexe). Le stade correspond à la deuxième période
critique. B gastrulation (blastodisque aplati). C gastrulation plus avancée (Ic champ
embryonnaire s'esquisse; organes axiaux non encore visibles). I) grossissement bordier
(Rand Knopf), première apparition des organes axiaux; le stade correspond à la troisième
période critique. E l'embryon formé s'allonge. Enveloppement du vitellus par lc blastodisque.
F stade de la fermeture du blastopore; le. stade correspond à la quatrième période critique.
la perche, à la suite d'un enveloppement plus rapide, la première ébauche
de l'embryon a lieu au stade de la fermeture du blastopore. A cette période
sensible dans le développement de la perche correspondent deux périodes de
sensibilité dans le développement du saumon. Par conséquent, le processus de
la formation des organes axiaux aussi bien que la fermeture du blastopore
sont corrélativement liés au changement de la stabilité des œufs.
Le petit tableau suivant permet de comparer nettement les périodes de
sensibilité des poissons qui frayent au printemps et celles du saumon.
Les périodes sensibles dans le développement des
P oissons.'
S a u in o n.
. Morula des cellules moyennes.
2. Commencement de la gastrulation.
3, • Stade du grossissement bordier (première ébauche de l'embryon).
3. Stade de fermeture du blastopore (ébauche du bourgeon caudal).
4. Période précédant l'éclosion.
7
246
Perch
1.
2.
3.
4.
Commencement of segmentation
Commencement of gastrulation
Anlage of axial organà (blastopore closure)
Has not been studied.
Starting with the formation of the caudal bud, the stability of the
eggs increases; it reaches a peak at the stage of eye pigmentation, then
again decreases during the period preceding hatching. According to
Hayes (1930), this is when fermenting substances that digest the membrane
of the egg do their damage to the embryo. Hayes' supposition was
confirmed by Schirkova, a student at our Faculty,and Solovieva, a student
at the Faculty of Zoology of the Herzen pedagogical institute. Premature
artificial hatching of the embryos ihcreases both their stability and
their rate of growth.
ACCLIMATION OF FISH EGGS EXPOSED TO HIGH TEMPERATURES
When fish eggs are exposed to high temperatures during their sensitivity
stages, it sometimes happens that one or two eggs do not die with the
others but remain alive much longer. This is because these surviving eggs
managed to reach the following, stable stage of their development: they were
able, as it were, to skip over the critical period. Fish eggs exposed to
a high temperature during their stable stages remain alive and continue
to develop for 60-70 hours. This persistence of development at high
temperature is astonishing since the eggs can reach the next critical
period in this amount of time even at a low temperature. At a high
temperature, development is much more rapid, and the embryo size shows that
the next critical period has long since been reached; and yet
the eggs do not die off. eggs exposed to high temperature at their
sensitivity stages (stage of blastopore closure) ordinarily die very
quickly; however, as we can see, if during the previous, stable period of
development the eggs have developed at a high temperature, they will be
much more stable at the stage of blastopore closure. At first we supposed
that‘ this was acclimation of a special kind. But microscopic analysis
of the preparation showed this supposition to be incorrect.
-
,
Aie.
LA DIFFÉRENCIATION ET LA CROISSANCE
24 7
D
tee egl
A
(-et/
;:k0.,.■• ■
!à-et
eZet,
'24
' 1
f
e.:.
ete-Développement de l'embryon du saumon à la t° de 19,5-2o 0 C. il stade auquel
les œufs furent placés à la haute température (enveloppement de 1/3 et plus}. 1? l'embryon
après un séjour de 14 heures à une température élevée. C embryon témoin de nième
dimension que B. D, E embryon aprZ.•s un séjour de 23 heures à une température élevée.
/: embryon témoin de nième dimension que 1) et E.
1
La figure 4, A montre un cruf au stade où il fut placé à une haute température. La figure 4, TI représente cet oeuf après un séjour de 14 heures dans
les conditions expérimentales. La comparaison de cette préparation avec un
embryon de dimension correspondante, mais se développant à bAsse température, permet de constater que l'embryon soumis à l'effet d'une haute température (préparation totale, colorée au carmin borique) ne présente pas la
di f férenciation de myototnes, qui sont parfaitement nets dans la portion
d'oeufs de contrôle (fig. 4, C).
Ti aurait été naturel de supposer que Von doit ce fait à la nécrose produite
à haute température. Or, ces embryons « nécrotiques » continuent à croître,
et encore 23 heures après ils atteignent des dimensions beaucoup plus considérables (fig., 4, D et E).
La. comparaison avec un embryon de dimension correspondante, mais se
développant à basse température (fig. D et F) montre que dam; ce cas
aussi la différenciation des myotomes se trouve empêchée. Les coupes microscopiques ont révélé dans les parties antérieure et postérieure de l'embryon
(2/3 environ de la longueur totale) une absence compli.ste de myatonies, bien
(lue la division cellulaire se poursuive avec beaucoup d'intensité..
Le croissance embryonnaire organisée se transforme ici en une multiplica9
per•• we'
•
,.m.ret*teee
4;;•
■
247
See photocopy next page.
Figure 4. Development of the salmon embryo at 19.5-20° C. A.Stage at
which the eggs were exposed to high temperature (yolk one third or more
incorporated). B.Embryo that has been kept at a high temperature for 14
hours. C.Control embryo of the same size as B. DE. Embryo that has
been kept at a high temperature for 23 hours. F.Control embryo of the same
size as D and E.
In figure 4, A shows the egg at the stage at - which it was exposed to
high temperature. B shows the egg after it had been kept under experimental
conditions for 14 hours. Comparing this preparation with an embryo of the
same size which developed at normal temperature, we can see that the
embryo exposed to high temperature (total preparation, stained with boric
carmine) does not show a differentiation of the myotomes, which are
perfectly distinct in the control eggs (figure 4,C).
It would be natural to suppose that this is due to necrosis caused
by hikh temperature. However, these "necrotic" embryos continue to grow
and 23 hours later have greatly increased in size (figure 4, D and E).
Comparison with an embryo of similar size developed at low temperature
(figure 4, D and F) shows that here too the differentiation of the myotomes
is inhibited. In the anterior and posterior parts of the embryo (about
two-thirds of the total length) microscopic sections revealed a complete
absence of myotomes, though cell division continues at a rapid pace.
Organized embryonic growth here turns into a completely unorganized
248
multiplication of cells, and this in turn leads to a greater stability of
the eggs. The harmful factor (high temperature) therefore eliminates
the more sensitive process of differentiation and maintains the process of
growth.
A similar phenomenon waS discovered back in the last century in the study
of bird development when the processes of growth and differentiation
véresuccessfully separated by means of abnormal temperature (Broca,
1862; Darest, 1876).
Tyler, working with echinid eggs, also tried to separate the development
of cell division by changing the temperature, but with negative results.
He does, it is true, say that it may be possible to separate these two
phenomena if we choose a different temperature, and that there is certainly
more hope of obtaining cell division without development, than development
without cell division. There is a large number of data on the first
situation in the literature (see above), but hardly any on the second
except in the writings of Fr Lilli (1902) on Chaetopterus, De Spek (1930)
on Nereis ) and Trifonova (1935) on the development of parthenogenetic fish
eggs.
4.
RATE OF GROWTH IN THE DEVELOPMENT OF THE SALMON EMBRYO
In the development of fish that spawn in the spring, the periods when
the embryo has a high resistance to harmful factors are also periods
of intensive growth (Trifonova, 1936). The question presents itself
whether trout development shows the same correlation between the growth
rate and sensitivity. A number of studies have described the growth rate
of salmonids (Kronfeld and Scheminzky, 1926; Gray, 1928; Privolniev,
1935), but all these writers fail to study the growth rate during the initial
period of development. The reason for this is perfectly clear: in the
first stages of development, the separation of the embryo from the yolk
and the parablast is delicate and this makes it difficult to obtain
reliable data. But we were interested specifically in the growth rate
at the start of development. Wetherefore ascertained the growth rate
of the embryo in three batches of salmon eggs (table II). We carried
out forty-one determinations of the dry weight of the embryo in the period
preceding the formation of the caudal bud, and fourteen determinations
at later stages, up to hatching (figure 2). The dry weight was measured
every day.
249
For each determination we made microscopic preparations. Since it was
impossible to separate the embryo from the yolk, we first fixed the eggs
with a twenty per cent formaldehyde solution. According to Scheminzky,
this fixation does not entail the loss of electrolytes and, as is known,
it preserves the glycogen. But even with fixed eggs, the separation
of the embryo from the yolk and most especially from the parablast is
far from easy, especially in the initial stages, when the embryo is small
and the parablast big.. We reduced the embryo to its dry weight (repeated
weighing until a constant weight was reached). Thirty-five embryos
were taken for each weighing.
The first series (table 2), done in 1935, shows the growth of the salmon
embryo from the stage of embryo formation (incorporation of the yolk) up to
and including hatching; his series shows a very rapid growthrateduring yolk
incorporation (Gv = 0.25, Gv = 0.12), and the complete cessation of growth
upon
blastopore closure (Gv = 0). A new increase in the growth rate
occurs toward the stage of eye pigmentation (Gv = 0.103), after which the
ùowth rate falls again and remains low until hatching (Gv = 0.02).
The second series (table 2) displays the growth rate of the embryo from
hatching until embryo formation. In this series, two or three measurements
of the dry weight were made at each stage of development, and yielded very
similar figures, according to which there is no increase in mass during
segmentation. The determinations were made at the start of segmentation
and at the morula stages of the morula of the large, average and small
cells. A very slight increase (Gv = 0.05) was noticed only toward the end
of segmentation. The start of gastrulation occurs so rapidly that if
determinations of the dry weight are made only once every twenty-four
hours during this pèriod they will not indicate the growth rate. The
growth rate reaches a peak at gastrulation, during the period preceding
the start of embryo formation (Gv = 0.62). When embryo formation begins,
the growth rate drops significantly (Gv = 0.15) even though relatively
speaking it is still fairly high.
Third series (1936) (table 2). This series starts with the gastrulation
stage and embraces the whole period of the - incorporation of the yolk.
Here, as in the preceding series, the growth rate is very high during
gastrulation until the start of embryo formation (Gv = 0.34). At the
start of embryo formation, the growth rate falls (Gv = 0.24), after which
it again rises during the final incorporation of the yolk, that is to say,
when the embryo begins to lengthen (Gv = 0.39). It then decreases again
when half the yolk is incorporated (Gv = 0.13).
250/251
Table II - Dry weight and growth rate of the salmon embryo (Salmo salar)
at different stages of development.
LEGEND
1
2
3
4
5
6
7.
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
5.
(see
photocopy next page),
Stage of development
First series, 1935
Second series, 1936
Third series, 1936
Average of the three series
Age in days
Dry weight of 35 embryos in mg
Log w
Gv
Start of segmentation
Morula of the large cells
Morula of the medium cells
Morula of the small cells
Start of gastrulation
Advanced gastrulation
Start of neural keel formation
Advanced neural keel formation
Yolk one-third incorporated
Yolk one-half incorporated
Yolk incorporation nearly complete
Blastopore closure
Start of eye pigmentation
Eyes fully pigmented
Hatching
GENERAL DATA ON SALMON EMBRYO GROWTH RATE
Kronfeld and Scheminzky, who started their study with the thirtieth
day of development, found two peaks of growth, the first, a slight one,
in the period preceding hatching, and the second, more marked,in the period
following hatching. Privolniev began his study with the third day of
development. His determinations for the start of development were rare
(4 for 23 days), and this makes them inconclusive.
He observed the same two peaks of growth as the first two authors, but
contrary to their findings, his first peak is higher than the second. In
addition to these two peaks, Privolniev observed a
250
A. N. TR I FONOVA, M. F. VER NI DOUIIE ET N. D. 1'1 I ILI PPOV
Tableau II. Poids ..;cc et rythme dc croissance de Pend»-von du
1
_
2.
S t a cl c s
du développement
Ageen
jours
lo
11
i.
Série
'
-35
sec e
me bryons Log. p. 1
en mg
,
I
Début de la segmentation
1
3
935
9 CV
II.
6
Age en
jours
Série,
nids sec de
35 embryns
o
1
4,4
3
6,2
,
-
4.4
Morula des cellules moyennes
--
--
-
Morula des petites cellules
-
-
--
-
--
-
6
,, ,
-
-
8
20,2
Enveloppement du vitellus
jusqu'à 1 /3
_
__.
Enveloppement du vitellus
jusqu'à 1 /2
_._
-
2o
2.1
Enveloppement du vitellus
. près de s'achever
14
16
42 ' 4 41 6
40,8
'
18
43- 2 41,4
22
Début de la plgt entation
des yeux
24
23
Yeux bien pigmentés
28
84,2
1,92531
37
to-S,5
2 ,03543
2,12385
13
14
- Début de la gastrulation
Gastrulation avancée
Début du Rand-Knopf
11
18
19
2.9
Rand-Knopf avancé
Fermetàc àt1 blastopore
Eclosion de l'embryon
.,
"r. -C - . . .:-
1,0899
• --,..)
20
t
0, 2 480
Ica
1
g. P•
0,64345
3.7 4,0
0,60206
4,0
4.0
0,60206
5
4.0
4. 8
4,4
0,64345
7
5.4
6,2
8.6
6,7
0,82662
12,0
12,5
13,0
1,09691
1 3 ,3 i.i 6
1,16435
8
-
1936
en mg
-
Morula des grandes cellules
St111111011
9
-
1,3 0 535
_
.
0,1224
__
_
--
-.
--
--
-
-
0,0546
0,0 54 6
0.0000
39.6
1,61189
61,8
t 1 .79099 •
0,1031
0-0773
47
133,0
53
6o
1 43.0
163,0
64
203,0
2.15685
2,21352
•
■
o,o3t7
.0.0203
0.0126
0,0187
.0.0546
2,30750 .
5. DONNÉES GÉNÉRALES RELATIVES AU RYTHME DE CROIS-
périt
SANCE DE I.T.AIIUn- ON DU SAUMON.
(lu d
étaie!
11
c(.2(lei
plu;
commencent leur étude à partir du 30KnoNFELD et ScilENI I NZKY,
jour du développement, ont établi deux sommets de croi.zsance - un, peu
marqué, à la période précédant l'éclosion, et un autre, plus important, à la
12
%.■
tur}er •
*
•,t‘
'
t
251
LA Dl FFÉREN C I AT ION ET LA CROISSANCE
sai1111011
(Saltno salar) aux différents stades de son. dévloppenient.
-
Af;e en
jours
Il. Série,
I9 3 6
Poids sec de
'8
1 . g . p.
35 embryons
en mg
2
3
5
7
? Cv
0,64345
4,4
3.7
4,0
4.0
4.0
4.8
5-1
4,0
0,60206
4,0
0,60206
4,4
(04345
6,7
6,3
8
'.
2480
.9
13,0
Log. p.
Log. p.
0,60206
_
-
-
4,0
0,60206
.-
4,0
0,60206
0,55630
4,4
0,64345
6,3
0,79 845
.-
I
3,5
"
--
-
7,0
0,85126
7,1
, 7,1
10,3
1,01284
13,1
1,11727
18,7
1,27152
25,4
1,40483
0,1202
0 , 245 1
1,16435
f4
11,6
1,06446
-
15
1 7,2
1 , 2 3553
0 ,3939
16
17
0,2261
7,3
12
0,1553
--
o 0000
0 ,493 6
0,3395
25,4
0,3898
1 ,4048 3
0,355 1
0,3 069
0,1359
0 , 1 359
1224
0,0000
0,0470
3,6 1,6
Io
_
■■•■•.
Cv
en mg
4,0
•
II"'
16.0 14' 6
35 embcyons
-
0,0470
1,09691
i Is sec de
9 cv
0,6223
12,5
Moyenne des 3 séries
-
_
0,82662
936
___
0,0000
0,2109
C,
'Pokls sec de
:)ge en
35 'embryons
jours
en mg
0,0000
8,6
I 2,0
s é I. i
Ili.
29,1
1 ,4 6 38 9
•
29,1
1,46389
0,1107
-
-
-
..103 I
-
-
,
'1.0000
1,62421
0,0000
-
•
.
41,6
--
-
4 1 ,4
1,61189
61,8
1 ,79099
,,
'. 0773
84,2
, •03 1.7
•
-
-
-
.0187
•
1,92531
108,5
2,03-543
1 33,0
143,0
2,12385
2,15685
163,0
2,21352
203,0
0,05466
0,1031
0,0773
0,0317
0,0203
0,0126
0,0187
0 ,0 54 6
0 5,16
0 .0 54 6
0,0546
UME DE CROIS-
I.: à partir du 30ance - un, peu
Jus important, iL . la
-
-
-
.-
période qui suit l'éclosion. PRivoi.xinv a commencé l'étude depuis le 3" jour
du déveloPPemeni. -'11-1 commencement du développement, ses déterminations
étaient rares (4 pour 23 jours), ce qui les rend peu concluantes.
Il a reconnu lès mêmes deux sommets de croissance que les auteurs précédents, mais chez lui, contrairement à leurs donnéès, le premier sommet est
plus haut que le second. Outre ces deux sommets, PRIvouNiEv en a constaté
13
_
M94g.X.P-'-lbtWeelffflinftioeleig,wfoltteeterepitieen
•
-
252
smaller peak between days 10 and 23 of development (petiod before
blastopore closure). According to our data, the period preceding embryo
hatching has three, not two, peaks of growth (figure 5) of which the first
is the biggest. Then the growth rate decreases as development continues
and this reduces the height of the following peaks (first Gv = 0.49,
second Gv = 0.35, third Gv = 0.0825).
Of our two peaks corresponding to Privolniev's first peak the first
comes in the gastrulation stage (before the start of ambryo formation)
and the second in the period in which the embryo has been formed and is
lengthening. According to Privolniev, the Gv of this period is 0.02,
but our findings make it very much higher (Gv = 0.45). This difference comes
from Privolniev's inclusion of the parablast in his determination
of the dry weight of the embryo. First, consequently, the weights he
obtained at the start of development are much higher than ours. (The weight
of thirty-five embryos at the third day of development is 17.3 mg
according to Privolniev and 4 mg in our figures) Second, Privolhiev
obviously could not determine the large increase in weight of the embryo
at the expense of the parablast, since he determined the total weight
(of parablast plus embryo). Our third peak is the first peak of Kronfeld
and Scheminzky and the second peak of Privolniev. For Privolniev, as for
us, this peak precedes eye pigmentation, and in his study this period comes
on days 32 to 35 of development, and in ours, on days 17 to 22. The
reason for this difference is that in Privolniev's study, hatching occurred
on days 70 to 75 whereas with us it occurred on days 56 to 60. A fall in
the rate of growth in the hatching period was found by Kronfeld and
Scheminzky, by Privolniev and by us.
When our data on the growth rate are compared with our sensitivity
periods of development, what immediately attracts our attention is the
intensive growth that marks the stable stages and the slower growth that
marks the sensitivity stages (figures 5 and 1). The growth rate is
especially high during gastrulation (stable stage), suddenly decreases
at the start of embryo formation (sensitivity stage), again increases
when the formed embryo lengthens (stable stage), then gradually decreases,
though still remaining high,up to the point where half the yolk is
incorporated. Subsequent incorporation leads to a fall in the growth rate,
and in the period preceding blastopore closure there is no growth at all.
At the same time, it is at this period that the eggs are most easily harmed
by outside factors. After this, when the caudal bud is already formed,
the growth rate of the embryo increases with its still increasing
stability. From eye pigmentation until hatching, embryo growth and stability
diminish, again concurrently.
253
See photocopy 'next page
Figure 5. Growth rate of the salmon embryo. --Days 1-5: segmentation.
--Days 6-7: start of gastrulation. --Day 8: advanced gastrulation.
--Day 9: first neural keel formation (Randknopf). :+-Day 10: advanced
neural keel formation. --Days 10-11: yolk one-third incorporated.
incorporation virtually
--Day 12: yolk one-half incorporated. --Day 13:
completed. --Days 14-16: blastopore closure. --Days 17-20: growth
of the tail. --Days 21-26: eye pigmentation. --Days 27-28: eyes well
pigmented. -- Days 56-60: hatching. The letters in the graph correspond
tb the stages in figure 3.
In the development of both salmon and fish thatspawnin the spring,
therefore, the growth rate and the sensitivity of the embryo vary in
an absol4te1y regular pattern.
The decrease in embryonic growth is explained differently by the various
authors.
Schmalhausen explains the decrease in the rate of growth during development
as due to the accumulation of differentiated plasma and of the products
of this diffeientiation. But this explanation can only apply to the gradual
decrease in growth as development proceeds. The sudden temporary decrease
in growth followed by another increase Schmalhausen explains as caused by
the presence of hormones which speed up or slow down growth, or by
products of metabolism that retard growth.
Kronfeld and Scheminzky attribute the fall in the rate of growth of
the salmon embryo in the period preceding hatching to the lack of water
caused by the slowness of water diffusion through the egg envelope.
253
LA DIFFÉRENCIATION El' LA CROISSANCE
v
4.___....
Increct■Se, ire- dry nu:Liter
Croissance du poids sec.
CM
Grotet il. ro-te_.
Rhuthme de croissance.
Mgr
1_,/4 200
,
.
190
0.-N
o
t80
S■
170
1..
180 c
"•
150
140 .L)
C)
13o E
I
0 O.
+Lu
g
/
1 • 110 i;-3 .
E
•<
/
,.
0 L
Z , • 80
.
an
2
A
tr 1r
I
0.1i
•
UMM
10
-
15
20
1
25
30
35
40
45
50
53
30
40
-1 30
20
10
Ca
Fig. 5. Le rythme de la croissance de l'embryon du sautnon. 1-50 jours — segmentation;
5-70 jours — conunencement de la gastrulation; Se jour — gastrulation avancée; 9r jour
— premier grossissement bordier (Rand Knopf); IO° jour — grossissement bordier, phase
avancée; io--ne jours — enveloppement du vitellus jusqu'au tiers; 12 0 jour — enveloppement du vitellus jusqu'à la moitié; 13e jour — l'enveloppement touche à sa fin; 34-16 0
17--2e jours -- croissance de la queue; 21-26e jours jours-femtdblaopr;
— pigmentation des yeux; 27-28e jours — les yeux sont bien pigtnentés; 56-6oe jours
— éclosion. Les lettres sur les figures correspondent aux stades de la fig. 3.
croissante. Après la pigmentation des yetrA et jusqu'à l'éclosion, la croissance
et la stabilité de l'embryon diminuent de nouveau parallèlement.
Donc, pendant le développement du saumon ainsi que des poissons qui
frayent au printemps, le rythme de la croissance et la sensibilité de l'embryon
varient d'une manière strictement rég -ulière.
La diminution de la croissance embryonnaire 'est expliquée différetnment
suivant les auteurs.
SCIIMALIIAUSEN explique la chute de la croissance au cours du développement par l'accutnulation du plasma dif férencié et de produits de sa différenciation. Cette explication ne saurait étre appliquée qu'à l'affaiblissement graduel
de la èroissance à mesure du développement. Quant au ralentissement provisoire assez brusque de la croissance accompagné d'un nouvel accroissetnent,
SCIIMALIIAUSEN l'explique par la présence d'hormones activant et retardant la
croissance ou par l'accumulation de produits du métabolisme- retardant la
croissance.
KR0NFEL.1) et SCHEMINZKY attribuent la chute de la croissance de l'embryon
du saumon dans la période qui précède l'éclosion au manque d'eau dit'à sa lente
diffusion à travers l'enveloppe de l'ceuf.
17. — A. Z. 1 939.
15
t
5
e;
4
1
I_
254
Gray explains the fall in growth at the end of salmon development
by saying that at the time the reserves in the yolk have been reduced and
the embryo is suffering from a lack of food at the start of independent
feeding.
Kronfeld, Scheminzky and Gray therefore explain the temporary slowdown
in growth by postulating not a change in the physiological state of the
embryo tissue caused by the process of development itself, but outside
factors such as lack of water or food.
Samalhausen tries to account for ther.temporary slowdown in growth by
saying that it is caused by changes in the embryo itself. Obviously,
however, the hormones stimulating or delaying growth cannot themselves
be the direct cause of variations in growth, but can be no more than
the mechanism that triggers the change in metabolism.
Trifonova (1936-1937) has shown that in the development of fish that
spawn in the spring, growth and differentiation occur with different
types of metabolism, so that during periods of growth, differentiation
is reduced, and vice versa.
6. GLYCOLYTIC PROCESSES IN THE DEVELOPMENT OF THE SALMON EMBRYO
In the development of the embryo of the salmon and of fish that spawn in
the spring (Trifonova, 1937), as well as in the development of the embryo of amphibia, (Brachet, 1935), measuring the glycolysis by the manometric method (by the
release of the extra C0 9 ) ijnot -pcissible bècause of the large alkaline
reserves. That is why the lactic acid anion has been measured by the
method of Furt, Charna and Catonio. The use of sodium metaphosphate
for precipitating the albumen in the salmon embryo gives unsatisfactory
results; we have therefore used sodium tungstate (2 ml of tungstate and
2 ml of 2/3 NH S 0) to -effect the precipitation. For the determination
2
of lactic acid, 17 eggs were used in each experiment. At the later stages,
the considerable increase in the mass of the embryo made it necessary
to use double the amount of tungstate for precipitating the albumen.
For each measurement, the lactic acid was determined in several batches
of control eggs. The amount of lactic acid was found to vary in batches
of salmon control eggs much more than in perch eggs, and also more than
in the blood, which is the substance used for the development of this
method. In order to avoid contradictory results as much as possible,
it was necessary always to distil the acetaldehyde for a strictly
determined period of time. Prolonging the distillation time can change
the results considerably.
255
In this case, it seems, other substances less volatile than acetaldehyde
begin to be distilled. We determined the lactic acid in two series
of experiments with salmon eggs and one series of experiments with trout eggs.
The first series (of determinations) was begun on day 6 of development,
at the gastrulation stage. Results are shown graphically in figures 6
and 7. Figure 6 shows the amount of lactic acid in 17 eggs at various
stages of development. Figure 7 shows the amount of lactic acid per 10 mg
of dry weight. The very clear difference between these two curves should
not surprise us since the mass of dry substance increases. According to
Bohrs and Hasselbach, the amount of oxygen absorbed by bird embryos
increases continuously, while the intensity of respiration (absorption
of oxygen per unit of dry weight) falls continuously. In this series,
the determination of lactic acid was carried out from the stage of
gastrulation (days 6..and 7 of development) until the period prior to
hatching (days 27-30 of development). The eggs in this batch were used
also for determination of the growth rate (first series) and of the
resistance of the eggs to high temperature (figures 1, 3 and 6). The
abterminationcf the differentiated sensitivity was started with these eggs
at an earlier stage, namely at the stage of segmentation (table 1,
series 4). In spite of the difference between the two lactic acid curves,
it is possible with both of them to follow the successive changes in the
amount of lactic acid during salmon development. These changes are
in perfect harmony with variations in the sensitivity of the eggs to
harmful factors. At the stage of gastrulation, the amount of lactic
acid is large; toward the stage of neural keel formation (days 8-9 of
development), it falls suddenly (this being shown by an arrow in the
figures), to increase again slightly, about the time when the yolk is one-third.
See photocopy next page.
Figure 6. Lactic acid in 17 eggs. First series. The letters on the
curve correspond to the stages in figure 3. For the day-by-day development,
see the caption of figure 5.
...
"."••
255
LA DIFFÉRENCIATION ET 1.A CROISSANCE
nient les résultats obtenus. Dans ce cas, semble-t-il, certaines autres substances
moins volatiles que l'acétaldéhyde commencent à se distiller. Nous avons dosé
l'acide lactique dans deux séries d'expériences avec des œufs de saumon et
dans une série ai.cc des œufs de truite.
La première série de déterminations de l'acide lactique fut commencée à partir du 6" jour du développement, au stade de la gastrulation.
Leurs résultats sont exprimés par les courbes des fig. 6 et 7. La fig. 6 montre
la quantité d'acide lactique aux divers stades de développement dans 17 œufs.
1.a fig. 7 donne la quanMr
1st 5e_rie5
tité d'acide lactique ra- C11 6 0 3
1 série
g
menée à 10 mg de poids
a
7
sec. La différence très
a
5
nette dans le caractère
.4
de ces deux courbes ne
1,3
1,2
doit pas nous étonner,
1.1
1,0
puisque la masse de sub0,9
stance sèche augmente.
0.7
0.5
Selon les dorntées de
0,5
lkinks et H ASSELBACII ,
04
0,3
la quantit..:. d'oxygène ab0,2
sorbée par l'etnbryon des
O 7 8 f) 10 11 1213 1415 16 17 18 19 20 2122 23 2425 26 27 2029 30 31 32
oiseaux s'élève tout le
Jours de développement
Do.y.S 0 F clevezp rwere
temps, tandis que l'inFig. 6. L'acide làctique dans t7 oeufs. Première série. Les
tensité de la respira- lettres sur la courbe correspondent aux stades de la fig. 3.
tion (absorption d'oxy- Pour le développement jour par jour, v. l'explication
de la fig. 5.
par unité poids
de
gèn
e
sec) tombe tout le temps. Dans sette série, les dosagts d'acide lactique furent exécutés depuis le stade de la gastrulation (6e et r jour
du développement) jusqu'à la période précédant l'éclosion (27-30e jour
du développement). Les œufs de cette ponte ont servi aussi à déterminer le rythme de la croissance ( l e série) et la résistance des œufs
à l'effet de la haute température (fig. 1, 3 et 6). La détermination de la
sensibilité différenciée fut commencée avec ces œufs à partir d'un stade plus
jeune — celui de la segmentation (tabl. I, série 4). Malgré le caractère différent des deux courbes de l'acide lactique, toutes deux permettent de suivre les
changements. successifs au cours du développement du saumon de la quantité
(l'acide lactique. Ceux-ci se produisent en conformité parfaite avec les variations
de la sensibilité des œufs à l'effet des agents détériorants. Au stade de la
gastrulation, la quantité d'acide lactique est grande, vers le stade du. grossissement bordier (8-9" jours du (léveloppement) elle tombe brusquement (sur
les figures cette chute est marquée par une flèche) pour augmenter de nouveau
quelque peu vers le temps où l'enveloppement du vitellus atteint le tiers
3
-
x•
t.
1 7•
t
17
•
•
•
.4
r11
:
7'
,••• " ;," • .
.
•
t
• „,
•
ma .
..e.,tire.âteeR
256
incorporated (days 10-11, second arrow). The stage of blastopanaclosureistherefore
characterized by maximum sensitivity to the harmful factors, by a
complete suspension of growth, and by a minimum amount of laCtic acid.
After the formation of the caudal bud (day 17 of development), the lactic
acid increases until the stage of eye pigmentation (days 23-25) (third
arrow) after which it decreases again and remains low until hatching.
This curve already shows that variations in the amount of lactic acid
correspond exactly to variations in the growth rate and in the sensitivity
of the eggs. Intensive growth and high resistance to harmful factors
correspond to a large amount of lactic acid, while a small amount of this
acid corresponds to low growth and hieh sensitivity. The correlation
data are especially convincing in this series of determinations,
See photocopy next page.
Figure 7. Amounts of C 3H 60 3 in salmon development (calculated for 10 mg
of dry weight). First series. For the explanation of the letters,
see figure 6.
256
A. N. TRIFONOVA, M. F. VER.NIDOUBE ET N. D. PHILIPPOV
jours, deuxième flèche). Donc, le stade de la fermeture du blastopore est caractérisé par une sensibilité maximum à l'effet des, agents détériorants, par la suspension complète de la croissance et par une quantité minimum d'acide lactique. Après la formation du bourgeon caudal (I7 e jour du,
(Io---u°
C3 116 03 Mgr
1,18
firs
. t
1,12
Série 1
1,08
1,04
1. 00
0.98
002 -21
0,88 '
•
0,84
1
0.80 .18
0.78
0.72
e.8 a
0.84
0.50
15
C
0.55
•052
12, v4
D
•
0.49
Ô
•
0
•
0.44
0.40
-
•
••
028
0.24
0.20
0.18
0.12
• .
6 E
cu
•17.
•
%
D
•
•
fet9 rwentoa- io YI
Pigmentation
des yeux
• •
0. 35
0.32
Eye.
6 \
•
‘■
•
•0.)
.2)
30
:5
0
1".5
•
0
0,05
■••
0.04
07 à 0 10 11 12 13 14 15 18 17 18 10 20 21 22 23 24 25 28 27 28 20 30 31 32
•
fDcLyI o F cle...vçar) rrue..."-Lt
Jours de développement
Fig. 7. La quantité de C.11603 dans le développement du saumon (calculée pour Io mg
de poids sec). Première série. Pour les désignations, v. l'explication de la fig. 6.
développement), la quantité d'acide lactique augmente jusqu'au stade de la
pigmentation des yeux (23-25° jours) ( 3e flèche), après quoi elle diminue
et -reste petite jusqu'à l'éclosion. Cette courbe montre déjà ‘ que les variations
île la qmintité d'acide lactique correspondent pleinement au x var ia ti ons d u
rythmedlacoisnte bilédsœuf.(Incroaeitsv
et une grande résistance des œufs à l'effet des agents détériorants correspondent ù une grande quantité d'acide lactique, tandis qu'a une pctite quantité
de cet acide correspondent une croissance faible et une haute sensibilité dcs.
œufs. La 'corrélation. constatée est particulièrement convaincante dans la préiS
'
•
-t•
•
'
• ■42-
-•'
•
• • ••"" .t.' ' • "
257
since the eggs of this batch have been measured simultaneously for
stability, lactic acid and growth rate.
Second series of determinations of lactic acid (figures 8 and 9).
Here, the determinations were started on day one of development and were
continued until day 19; they covered the whole of development up to the
stage of blastopore closure. The first decline in the lactic acid level
(shown by an arrow on the figure) came on day 5 of development and corresponds
to the morula stage of medium cells; during this stage, as we have already
pointed out, the resistance of eggs to harmful factors is also lowered
(page 244, figure 1). The second fall in the lactic acid level comes at the
stage of the passage to gastrulation (figure 3A); the third at the start
of the formation of the neural keel (Randknopf) (figure 3D) and the fourth
in the period preceding blastopore closure.
Like the first series therefore, this series shows a perfect correspondence
of variation between the amount of C - H 0 the growth rate and the resistance
3 -6 3 '
of the eggs to harmful factors.
See photocopy next page.
Figure 8. Variation in the amcunt of lactic acid in 17 eggs (second series)*-Morula of medium cells. The other stages of development are indicated by
letters on the curve (A,B,C,D,E,F ).
The stages are shown on figure 3.
Figure 9. The amount of
in salmon, :development (calculated per
C3H603
10 mg of dry weight). Second
series. For explanation of the letters, see
figure 8.
257
LA DIFFÉRENCIATION ET LA CROISSANCE
sente série de déterminations, vu qu'avec les oeufs de cette ponte on a exécuté
:simultanément des déterminations de la stabilité, de la quantité d'acide lactique
et du rythme de • a croissance.
Seconde série de déterminations de l'acide lactique (fig. 8 et 9). Dans
cette série, les dosages furent commencés dès le premier jour du développement et poursuivis jusqu'au 19e jour; ils ont embrassé tout le développement
C3 11 6 03 ko kAes
Mir heures
3.0 1-36 •
2.9
2.8 r33
2.7
2,6
2.5 -30
2.4
2.3 -27
22
2.1
2.0 .24
1,9
1.8 -21
1.7
1.8
1,5 '18
1,4
1.3 -15
0
C 3 H8 03
Dépérissement
des oeufs
-
ri me.
Seconci
2 série
,
1,2
1,1
1 I 3 I. 3 ê7 8 1 KIIII21314 1313111819
Jours dé déwhappaZeto
Fiinc.:ug. Variation de Ia quantité d'acide lactique dans 17
œufs (deuxième série) * —
morula des cellules moyennes. Les autres stades de
développement sont marqués
par des lettres placées sur la
courbe (A, 13, C, D, E, F);
les stades sont représentés
sur la f ig. 3.
1.0 -12
0.9
0.8
0,7
0.6
0.5 6
0.4
0.3
3
02
0,1
1 2 3 4 5 6 7 6 9 10 11 12 13 I4 15 18 17 18 10 20 21
Jours de deyeloppereent
eCt.r13 01- Cle.A.i.eireraRre
Fig. 9. La quantité de C31-1603 ans le dé-
veloppement du saumon (calculée pour to
mg de poids sec). Deuxième série. Pour les
désignations, V. l'explication de la fig. 8.
jusqu'au stade de la fermeture du blastopore. La première diminution de
l'acide lactique (ce moment est marqué sur la figure par une flèche) tombe
sur le 5" jour du développement et correspond au stade morula des cellules
moyennes, pendant lequel, comme nous l'avons déjà signalé, la résistance des
œufs à l'effet des agents détériorants se trouve également réduite (p. 244,
t). La seconde diminution de l'acide lactique correspond au stade du passage à la gastrulation (fig. 3, A); la troisième au début du grosissement
bordier (Rand Knopf) (fig. 3, D) et, enfin, la quatrième tombe sur la période
précédant la fermeture du blastopore.
De cette manière, cette série a montré, comme la première, une correston-
dancc parfaite de la variation de la quantité dc C 3 11 60,, du rythme de la
croissance et de la résistance des crufs aux effets des apents détériorants.
19
•
•
• se.,
9•011.3
.
••• ••• ••■•■•■••■•••■
258
7.
RESPIRATION DURING EMBRYO DEVELOPMENT OF THE SALMON
Method. In each experimen4, we measured respiration simultaneously
in two Warburg spirometers, Each spirometer could hold 35 eggs. When
the eggs are placed in the spirometer containing water, it is necessary
to shake the spirometer evenly so as to obtain a gaseous equilibrium
between water and air. Since the large salmon eggs are damaged by shaking,
the eggs were placed in the spirometer in a humid atmosphere and respiration
was recorded without shaking. During these experiments the temperature
was kept at 10 °C.
Experiments were carried out daily and were made to last as long as
possible (10-15 hours), because when the eggs are transferred from the
water to a humid atmosphere, a gaseous equilibrium is not established for
2 to 3 hours. Measuretents made when there was no gaseous equilibrium
were ignored. Respiration was measured every hour. In each experiment,
some eggswere fixed and examined under the microscope. The curves
absorbed in one hour - by 35 eggs and by 5 mg dry
show the amount of
P2
weight of embryo.
Experimental data. The rate of respiration of the salmon embryo is
very low; this is why in the first stages of development, when the mass
of the respiring eggs is very small, it is very difficult to obtain
reliable results. This difficulty was noted also by Schlenk (1933). We
carried out three series of experiments to measure respiration. Oneseries was carried out in 1935 'and two in 1936.
Segmentation. In this stage, respiration was measured most comprehensively
in the second series of experiments (figure 10). During segmentation,
respiration is very low. In days 3, 4 and 5, of development we not only
could not detect any 0 absorption but in all the experiments the eggs
2
released a gas that was not absorbed by the alkali so that the manometers
showed an increase in pressure. From the 0, absorption it could have been
supposed that at the start of the developmeit, metabolism was very low;
indicate that vigorous
but the findings from the determination of
C3H603
anaerobic processes of fission occur here.
Consequently, segmentation and the increase in the number of cells occur
largely at the expense of the fission processes. Thatcell division takes
place in anaerobic conditions has been known for a long time (Godlewski, 1901;
Lipmann, 1933). Some data also suggest that C3H603s released during
division (Rapkin, 1927, 1930). The release of an acid during segmentation
was observed also by R Lilli (1931).
259
Toward the end of segmentation, in the period that precedes gastrulation
(figure 3, A) respiration increases rapidly. The increase in respiration
at this stage was found in all three series of experiments. In the first
series, the respiration rate at this stage (absorption of 0 2 per hour per
5 mg) is 7.4 mm in the second series it is 5.8 mm 3 and in the third
series 10.6 mm 3 .
,
At the stage of the passage to gastrulation, therefore, anaerobic fission
and respiration show the interrelation-required by the Pasteur-Meyerhof reaction:
an intensification of respiration accompanied by a decrease in the amount of C 3 H 6 0 3 .
Gastrulation (In the period preceding embryo formation, figure 3, B, C ).
If the Pasteur-Meyerhof equilibrium undergoes a clear shift toward the
oxidation processes in the period prior to gastrulation, it undergoes an equally
clear shift in the opposite direction during gastrulation. At this stage, as
level is high while an attempt to measure the
has already been said, the
C3H603
is so much reduced that the oxygen
the
respiration
respiration showed that
method
used (the rate of respiration
the
absorption could not be recorded by
equals 0). There is then a positive, not a negative pressure in the spirometers,
just as there was during segmentation. This fall in respiration at the gastrulation
stage is very marked on all curves (figures 10, 11, 12).
Embryo formation. At the stage of neural keel formation (Randknopf) (figure 3,
D; third series of experiments, figure 12), the intensification of respiration
can be seen clearly (rate of respiration 2.5). This intensification ceases as
soon as there is one-third incorporation of the yolk. As stated in the previous
paragraph, the stage of neural keel formation is marked by a low C3H603 level
which suddenly increases when the yolk is one-third incorporated. Here again,
therefore, strong respiration is linked to low amounts of C3H603'and vice versa.
On the curve of the first series, the intensification of respiration at the neural
keel formation stage is not expressed, perhaps because in this series respiration
was not measured on day 10 of development (figure 11). As has already been shown,
respiration decreases markedly when the embryo lengthens (figure 3, E) (one-third
incorporation of the yolk).
At this point, the spirometers do not register oxygen absorption (the PasteurMeyerhof equilibrium shifts in the direction of more intense processes of anaerobic
fission) (figures 11 and 12).
At the start of the salmon development we therefore have three periods
in which respiration temporarily falls so low it is absolutely impossible
to record any oxygen absorption. This temporary cessation of respiration
occurs during segmentation, eastrulation and the incorporation of the first
third of the yolk.
See photocopy next page.
Figure 10. Rate of respiration of the salmon embryo. First series -oxygen absorption per hour of 35 eggs. The broken line shows oxygen
absorption per hour of 5 mg dry weight. The stages are indicated by letters
placed over the curve (A.B.C.D.E.F). The lack of measurements at stage D
is shown by a dotted line with a question mark over it.
During these periods, as we have seen earlier, the spirometers show a
positive pressure, indicating that gas is released. When the eggs are
taken from the water and placed in a humid atmosphere, they continue to
release oxygen for two or three hours, until there is a gaseous equilibrium,
but during the three stages in question, release of gas does not stop
after that time but continues for as long as the experiment lasts
(9-12 hours). Oxygen absorption starts only at the moment when the eggs
in the spirometer begin to die, but it is not accompanied by a release of
carbon dioxide. The tempory cessation of oxygen absorption and the
release by the developing egg of a gas which is no eabsorbed
260
A. N. TRIFONOVA, 1\1. F. VERN1DOUBE ET N. D. PHILIPPOV
Nous avons donc au commencement du développement du saumon trois
périodes où la respiration tombe temporairement jusqu'à un niveau si bas,
qu'il est absolunzent impossible d'enregistrer une absorption d'oxygène. Cct
arrêt momentané de la respiration tombe sur la segmentation, le stade de la
gastrulation et la période de l'enveloppement du vitellus jusqu'à son tiers.
rt.r5t 5e-rie5
1 série
•
1
MM 3 02 IO
9
8
7
6
5
4
3
2
A
9
B
%
\...."
%%.
er .......?• • • mr, F
t-
.
,...... ■-- - Ir - - - -/t- - *- - •
•
8
0
ID
II
12
Jours de développement
13 14
Dcuti5
.....
.
15
16
17
18
19
21
22 23 24
eç d e,ve.tern.e,e.t
Fig. io. Le rythme de la respiration de l'embryon du saumon. Première série de l'absorption d'oxygène en une heure par 35 oeufs. La ligne pointillée indique l'absorption de 03 en t
heure par 5 mg de poids sec. Les stades sont marqués par des lettres placées sur la
courbe (A, B,. C, D, E, F). L'absence de mesurage au stade D est marquée par une ligne
interrompue et par un point d'interrogation.
A ces périodes, on constate dans les spiromètres, comme nous l'avons vu
plus haut, une pression positive, ce qui accuse un dégagement de gaz. Quand
on transporte les oeufs de l'eau dans une atmosphère humide, ils dégagent
toujours de l'oxygène pendant deux ou trois heures, jusqu'à . l'établissement
de l'équilibre gazeux, mais à ces stades-ci le dégagement du gaz ne cesse pas
après ce terme et se poursuit pendant tout le temps que dure l'expérience
(9-12 heures). L'absorption d'oxygène ne commence qu'au moment où les
reufs placés au spiromètre commencent à dépérir, niais elle n'est pas accompagnée de dégagement d'acide carbonique. La suspension de l'absorption
d'oxygène et le dégagement par l'ceuf en voie de développement d'un gaz que
22
•
.•
:S1,4 ; •
4
'
261
by an alkali are certainly so paradoxical that they must be verified and
further investigated. At present we can only report that Brachet (1934)
observed an increase in rh and a livid color in axolotl eggs placed
with colourless methylene blue in an atmosphere without oxygen. On the
other hand, as early as 1830, Dalk found that the gas in bird eggs contains
6% more oxygen than the surrounding atmosphere. Another investigator
of the metabolism of bird eggs (Hasselbach 1900, 1902) was led to conclude
from numerous experiments that a slight amount of gas other than carbon
dioxide is released by the developing egg. Hasselbach believed that this gas
consists of oxygen and hitrogen. He tried to verify this curious
phenomenon by various methods and found that it was consistently
repeatable.
Hasselbach supposed that in the first hours of development, there is
here a physiological secretion of 0 2 which is linked to the processes
of assimilation or constitutes a byproduct of fermentation reactions.
Brandes (1924) returned to this problem and supposed that the oxygen
that is released is very important for the egg, separated as this is
from the surrounding air by the albumen and the shell. Needham (1931)
pointed out that chicken eggs contain an active catalase; he thought it posssible
that the release of oxygen by the egg is linked to changes in the 111 0, level
and in enzyme activity.
'
•
.i•J
It has not yet been determined whether in the development of salmon
eggs there is intramolecular respiration in those stages where there
is a visible temporary cessation of respiration. It seems that in a
spirometer without alkali there is a slightly greater pressure which may
be the result of the release of not only 0 but also CO . However,
2
2
261
LA DIFFÉRENCIATION ET I.A CROISSANCE
l'alcali n'absorbe pas sont certes un phénomène si paradoxal qu'il exige
(l'être vérifié et approfondi. A l'heure qu'il est, on peut seulement signaler . que
BRACHET (1934) a observé dans les œufs de l'axolotl placés dans une atmosphère sans oxygène dans du bleu de méthylène leucotomie une hausse du
rh et une couleur livide. D'autre part, encore en 183o DALx a trouvé que dans
l'oeuf des oiseaux le gaz est de 6 % plus riche en oxygène que l'atmosphère
ambiante. Un autre investigateur du métabolisme de Ikeuf des oiseaux (l'AssEmActi, 1900, i902), à la suite de ses nombreuses expériences, a abouti à
la conclusion qu'une quantité peu importante d'un certain gaz autre que l'acide
carbonique est dégagée par l'oeuf qui se développe. HAssELP.Acti croit que
MM 3 02
11
10
MM3 02
8
7
Stdseries
2 série
45
ateunl de dleaeleepen.n1
IDCa.j5
CF
6
a
7
8
sl 13-C
9
eNi ZÀ,CIFFIVZ.rtt
ID
II
Jeeen de orwccor,m
12
•
13
14
15
16
Dc,AJS o f devez:1 rn.e._.evt
Fig. 12. Le rythme de la respiration de
l'embryon du saumon. ,I lètnes désignations qu'à la fig. to.
Fig. It. Le rythme de la respiration de
l'embryon du saumon. Deuxième série;
mentes désignations qu'à la fig. Io. * —
segmentations.
1
3 série
8
7
6
5
4
3
2
ce gaz est l'oxygène et l'azote. Il a tenté par diverses méthodes de N'érifier
ce curieux phénomène, et celui-ci se répétait chaque fois.
HASSE1.11ACII émet la supposition qu'il s'agit ici d'une sécrétion physiologique
de 0 2 durant les premières heures du développement, sécrétion liée aux processus d'assimilation ou constituant un produit accessoire des réactions fermentatives. BRANDES (1924) revient à cette question et estime • que l'oxygène
qui se dégage a une grande importance pour la vie de l'oeuf, séparé de l'air
atmosphérique par l'albumen et la coquille. NEEDHAM (1931) fait ressortir
que les oeufs de poule contiennent une catalase active et croit possible que le
dégagement .d'oxygène par l'oeuf se trouve lié au changement de la concentration de RD, et au changement de l'activité de l'enzyme.
On n'a pas réussi à établir, dans le développement des (cuis de saumon,
si aux stades de suspension N'isible de la respiration il se produit une respiraque dans un spiromètre privé d'alcali il y ait
l
tion . intramoléculaire. Il sem..).e
une augmentation quelque peu plus forte de la pression, qui est peut-être le
résultat du dégagement non seulement de 0,, mais aussi de CO,, mais la
23
J
262
the difference is so small that it may be within the limits of error
due to methodological inaccuracy.
While the respiration is reduced temporarily to nothing at the period
of the first lengthening of the embryo, it begins to increase during the
later incorporation of the yolk, toward the stage of blastopore closure,
and continues slowly to increase until the appearance of the first eye
pigmentation, when it reaches a rate of 2.8. At the stage of the blastopore
closure therefore, the Pasteur-Meyerhof equilibrium shifts in the direction
of stronger oxidation activity. This period is marked also by complete
suspension of growth, and appears to be the period in which, in the whole
of embryonic development, there is the greatest sensitivity to harmful
factors.
This shift of the Pasteur-Meyerhof equilibrium in the direction of
stronger oxidation activity, as it is oberved in salmon developmene, is
always accompanied by a fall in the growth rate and diminished egg
stability. At the stage of eye pigmentation we have a visible . contradiction,
as respiration increases(though very slowly) but nevertheless the stability
of the eggs and their growth rate also increase very distinctly. It goes
without saying, however, that we cannot assess the displacement of the
Pasteur-Meyerhof equilibrium by measuring only one of the processes of
which it consists (respiration or glycolysis).
At the stage of eye pigmentation, respiration increases, but as the
have shown, the fission processes are then also
dèterminations of
C3H603
active. As a result glycolysis increases so much that in spite of the
increased respiration not all the C.11-10 1 that is formed can be resynthesized
so that the Pasteur-Meyerhof equiliriuM is still shifted in the direction
of more intense anaerobic fission activity.
Growth which is based on the synthesis of protoplasmic masses drawn from
the yolk requires a very considerable expenditure of energy.
It is therefore natural that during the intensification of growth,
the shift of the Pasteur-Meyerhof equilibrium in the direction of
anaerobic fission (constituting an energy resource for growth) can occur
against the background of a general increase in the metabolic rate.
When the Pasteur-Meyerhof equilibrium shifts in the opposite direction,
morphological differentiation occurs. In the development of the perch
(Trifonova, 1936) and the salmon, this takes place through intensified
respiration. It may be asked whether respiration is an energy resource
for differentiation.
263
The question of the relation between morphological differentiation
and energy expenditure has been debated for a long time.
In 1933-1935 Tyler expressed his conviction that energy was necessary
for development. His experiments showed that an embryo coming from half
or a quarter of an egg absorbs more oxygen to reach a given stage of
development than a normally developing egg, and this greater absorption
is broughtabout not by an increase in the growth rate (which is exactly
the same in dwarf and normal embryos), but by a slowing down of development,
that is, by an increase in the. period of respiration. Giant embryos
(resulting from the fusion of two fertilized eggs) on the other hand,
develop more rapidly than normal embryos. These facts Tyler consider s .
as proof that energy is consumed in differentiation, since in his opinion
the development of two "halves" of an embryo requires more differentiation
activity than the de*elopment of one whole embryo. But this argument is
open to a host of objections. First, Tyler did not measure the respiration
rate of giant embryos. Second, he did not even explain completely
why the development of one whole embryo from half an egg requires more
work than the development of half a normal embryo. Third, the slowing
down of development can certainly be due to other causes than the necessity
of accumulating a certain amount of energy during development. This is in
fact stated by the author himself in an article published in 1937.
In our opinion, Tyler's fine experiments have no direct bearing on the
question of energy and differentiation.
Besides Tyler, a number of experimenters have tried to find energy
that is consumed in differentiation, to discover an increase in the energy
potential of differentiated plasma.
However, except for the isolated findings of Lepeschkin (1929, 1930),
no "structural energy" has been discovered. It is therefore possible
that the intensification of respiration is necessary for the process of
H
0 , decreases the
differentiation only because it eliminates the
C3 63
active reaction and thereby causes the aggregation or the protoplasm
to become more loosely distributed. If that is so, respiration has the
same function in embryo development as it has in muscular contraction.
Respiration is not an independent energy resource, but is used only for
the resynthesis of C 111 40 1 , which accumulates when the muscles work,
making them sluggish; an dwhich impedes the process of differentiation
in embr7o development, by making the protoplasm coarser in structure.
Runnstrôm (1930) has pùt forward the hypothesis that in
embryonic tisbue, vafiations- of metabolism and variations in
264
protoplasmic structure go hand in hand, a variation in one causing a
variation in the other. Runnstrgm believes that the increased concentration
of hydrogen ions is linked to a reduced dispersion of the protoplasm
(observation made in the dark area). Makarskaia, a student at the
Ichthyological Laboratory of the State University of Leningrad, working
under the direction of Trifonova, has determined the adsorbing properties of
the protoplasm of the perch embryo at the stages of growth and differentiation.
Her findings clearly show that periods of growth (periods of increased
protoplasmic acidity) are linked to an increase in the adsorbing
properties of the protoplasm. This definitely means that periods of
growth and differentiation are characterized not only by a different
metabolism, but also by a different state of the protoplasm. The
accumulation of hydrogen ions during the processes of growth leads to
changes in protoplasmic structure and to increased adsorbing ability,
and these structural changes, by increasing the heterogeneous catalysis,
must bring about an increase in metabolism. It is therefore natural that
metabolism should be higher during growth (stage of eye pieentation) and can
be lower during differentiation.
There is a parallel between the state of embryonic tissue at the period
of intensive growth and the state of the tissue in reversible deterioration,
which has been described by Nassonov and Alexandrov (1936,1937) and which
they called "paranecrosis".
8.
GENERAL CONCLUSIONS
Schmalhausen, while studying the growth rate during development of the
chick, has found that growth does not slacken gradually, but is particularly
slow at some periods, after. whièh it again increases, and then falls
once more. According to Schmalhausen, increased growth leads to a
weakening in differentiation and vice versa.
In the first part of this study, Trifonova mentioned that, according to
Schmalhausen, the maximum rate of growth was observed at the start of
development. I.I. Schmalhausen, in a personal letter to Trifonova, stated
that he was referring not to the start of the development of the egg, but
only to the start of the growth of the formed embryo.
A similar alternation between periods of reduced and increased
growth has been observed in the development of fish that spawn in the
spring, in which the growth rate parallels the sensitivity of the eggs to
.■
—1e.
265
t.
harmful factors and the type of metabolism (Trifonova, 1935, 1937).
In these studies, variations in growth, sensitivity and metabolism were
found to depend on the processes of morphogenesis that occur at this time,
exactly as Schmalhausen had found in his investigations.
Growth occurs when the Pasteur-Meyerhof equilibrium shifts in the direction
of the anaerobic scission processes, which are an energy resource for growth.
Differentiation processes occur when the Pasteur-Meyerhof equilibrium shifts
in the opposite direction (Trifonova, 1937).
An article of Ajsupiet (1937) suggests that a similar change in metabolism
occurs during the processes of growth and differentiation in the regenerating
hydra. According to Ajsupiet, at the start of the operation the hydra absorbs
less oxygen than usual, following the intensive growth that takes place at the
expense of the scission processes. In the periods where oxygen absorption
increases, we can assume that processes of differentiation are taking place in
the hydra organism.
The antagonism between the growth rate and differentiation postulated by
Schmalhausen and confirmed by various authors (Irichimovich, 1936: metamorphosis
of amphibia; Streich and Svetosarow, 1937:
growth of the chick; Trifonova, 1937:
development of the perch) are explained, it seems to us, by the fact that these
processes take place in the presence of various types of metabolism. It follows
that these processes weaken each other, but also condition each other. This
interdependence is due to the historical evolution of the particular species.
During ontogenesis, this interdependence is manifested in the fact that the
accumulation of lactic acid when growth processes are predominant stimulates an
increase in respiration and triggers the start of differentiation; and again e in
the fact that the elimination of lactic acid in the period of differentiation
lowers respiration and increases glycolysis and the growth rate.
Since in fish that spawn in the spring (perch, ruffe) growth inhibition
and changes in sensitivity and metabolism are caused by an intensification of the
processes of differentiation, and are linked to specific stages in development,
it is to be expected that in related species, too, these stages of development
will show a slackening of the growth rate and a corresponding sensitivity increase
and metabolic change.
The present study has demonstrated that in both the salmon and the perch
there are variations in growth, metabolism and sensitivity at the start of
gastrulation and of embryo formation and during blastopore closure. A
particularly interesting finding was that artificial inhibition