KOFOID: DEVELOPMENT OF LIMAX. 47 
have no limiting membrane ; they are, however, devoid of the granular 
structure of the surrounding protoplasm, and are the centres about 
which the radiations constituting the asters are arranged. 
The position of the astrocols with reference to the nuclei is worthy of 
note. 'lhey are removed some distance from the nuclei toward the 
animal pole of the cells in which they lie. A comparison of this figure 
with that of a later stage shown in Figure 5 indicates that the astroccels 
are migrating toward a region where later the nucleiare found. It must 
seom therefore from the conditions in Figure 14 that the nuclei are pre- 
ceded in this migration by the astrocoels. This recalls the shifting of 
male and female pronuclei attributed to the astrocols by Conklin (94) 
in Crepidula. 
In the living egg of this stage, when the cells have reached a perfectly 
spherical shape, each blastomere seems to bo entirely independent of 
the other, and not the least trace of any contact or connecting proto- 
plasm ean be detected between them. Each has a definite, unbroken 
contour, and in most cases there is an appreciable space between them, 
which shows no differentiation from the surrounding albumen. In the 
egg shown in Figure 14 the separation is not so great as it apparently is 
in the living egg. It is an interesting phenomenon, and raises the ques- 
tion as to the existence of any actual protoplasmic connection between 
the blastomeres in the stage following constriction. Tt is impossible to 
answer the question satisfactorily from observation of the living egg, 
for there is the possibility of the existence of a thin sheet of protoplasm 
which, on account of its transparency, thinness, and optical resemblance 
to the surrounding albumen, cannot be detected. The egg shown in 
Figure 14 was shelled by the process described in the preceding pages, 
and washed free from the albumen by normal salt solution, transferred 
in eapillary tubes a number of times in the process of preparation, and, 
after mounting in balsam, was rolled over in various directions repeatedly 
without a separation of the two blastomeres. The two cells have each of 
thom a definite and sharp outline at all planes of focusing, and even 
under high powers of the microscope no deeply stained granular bridge 
of protoplasm can be detected between them. It is only by very care- 
ful focusing that the rather vague, transparent, unstained connection 
between the cells can be seen. So far, then, as this preparation goes, it 
shows that there is a physical band of connection between the two 
blastomeres in this stage of greatest separation. The nature of this 
connection is problematical. It may be the Schleimschicht of Warneck 
(50), or it may be a continuation of the “ differentiated superficial 
