THE EFFECTS OF HYPEUTONIC SOCU'J'IOXS. 
463 
Fig. 52 shows the normal condition of a nucleus before the 
break-up of the nuclear membrane. Thirty-eight chromosomes 
can be identified, although the exact number is often difficult 
to determine, owing to portions of individual chromosomes 
occurring- in two sections of the same nucleus. There are 
typically no vesicles. Just as in the other series of eggs, 
however, exceptions are found (figs. 53-55). The large vesicle 
in fig. 53 has a peculiar structure, and which, as is suggested 
above, may have arisen from more than one centre, there- 
fore, being equivalent to more than one chromosome. 
Fig. 61 shows an anaphase, with the chromosomes some- 
times very irregular in outline. In the centre of the spindle 
is a large vesicle, the interior of which is practically un- 
stained, Avhile round its periphery are a number of minute 
dark dots. 
Later Stages in the Development of “Hypertonic” 
Fg-srs . 
The eggs of E. esculentus which have been treated with 
hypertonic solutions of moderate strength usually behave 
quite normally until after the first cleavage has been com- 
pleted; only a few exceptions were found in Avhich the first 
two blastomeres were unequal. After this, segmentation 
usually becomes irregular, and gives rise to blastulae such as 
are figured (Text-fig. 3). Great mortality occurs at this stage ; 
only a few gastrulae were obtained, and these were more or 
less abnormal and never gave rise to plutei. 
“Hypertonic” eggs of E. acutus show a somewhat 
similar development. Text-fig. 4 represents irregular blas- 
tulae from these cultures. The development is i-etarded con- 
siderably by treatment with the solutions. The first cleavage 
is normal in all the eggs which develop, even in the case of 
eggs treated with 50 c.c. sea-water -t- 15 c.c. 24 M. XaCl 
solution. The later segmentation of such eggs is irregular 
in all the cultures; and the number of these abnormalities 
varies roughly from 1 to 20 per cent, of the total number of 
