70 BULLETIN OF THE 
to be of considerable thickness, and to envelop closely the peripheral 
layer of yolk corpuscles. An enlarged view of the same, given in 
Figure 30, Pl. VI., shows the finely granular structure and the vesiculated 
condition of the hardened blastema. It also shows how the blastema fits 
over the yolk corpuscles, and dips down between them. It is to these 
depressed regions that the boundary lines of the polygonal areas are due. 
Figures 31-33 are enlarged views of separate yolk corpuscles with the 
accompanying blastema. 
The protoplasm of the blastema has a very characteristic appearance, : 
In addition to the common character of being very finely granular, the 
protoplasm is throughout finely vesicular or spongy. The latter charac- 
teristic is especially marked in eggs heated in water to coagulate the pro- 
toplasm, and arises, I think, in the following manner. The fat globules 
described as filling the protoplasm of the blastema in the fresh egg are 
dissolved in the alcohol used for hardening purposes, and consequently 
leave in the protoplasm spheroidal spaces of nearly uniform size, which 
constitute the interstices. A discussion of the cause of the division of 
the blastema into areas will be found under general considerations at the 
end of the paper. 
I have been unable, for the want of material, to trace the final changes 
in the germinative vesicle. In the earliest condition of the deposited 
egg that I have been able to procure there is a single central nucleus 
(Figs. 28, 29 nl.), which is doubtless the descendant of the germina- 
tive vesicle. This is the first segmentation-nucleus ; it is large, oval, 
very finely granular, and surrounded by a spheroidal mass of protoplasm. 
The latter is in immediate continuity with the network of protoplasm, 
which extends throughout the egg. The yolk corpuscles in the vicinity 
of the protoplasm, which envelopes the nucleus, are much broken and 
become successively smaller in approaching the nucleus, and at length 
appear to merge into the finely granular protoplasm. 
In the succeeding stage the central nucleus divides into two of equal 
size, which occupy a sub-central position (Fig. 34, n/, ni’). These nuclei 
have essentially the same character as the one already described. Fig. 36, 
from a two-cell stage of another egg, shows one of the nuclei with a cen- 
tral vacuole (v/.). The yolk is rudely divided at the same time, and 
having been previously arranged in radiating branched columns (Deuto- 
plasmasdulen of Ludwig), now forms two groups of such columns (Fig. 34). 
It is probable that each of the two nuclei is divided into two others, 
and that each resulting therefrom is similarly divided, but I have not 
seen the four-cell stage. The next stage sectioned is one with eight 
