184 ADAM SEDGWICK. 
nuclei in a condition of structure somewhat different from that 
usually presented by nuclei? or are the nuclei of the endoderm 
cells derived from the nuclei of the ectoderm by migration 
from the latter at the disco-gastrula stage? The continuity 
between the reticulum of the endoderm and ectoderm cells is 
retained as I have said through the disco-gastrula stage (fig. 
16) to the gastrula stage (figs. 20, 24—26) ; indeed, in the 
gastrula stage it becomes, in consequence of the closer approxi- 
mation of the endoderm masses to the whole inner surface 
of the ectoderm cap (fig. 20), still more marked. The strands 
of the reticulum of the ectoderm cells are continued into the 
strands of the ectoderm masses, and the whole ovum presents 
the appearance of a multi-nucleated vacuolated mass (fig. 20). 
It may be that some of the nuclei of the ectoderm cells pass 
along these continuous strands inte the endoderm. But against 
this view are these two facts: (1) I have never seen any trace 
of such a migrating nucleus, and (2) the structure of the 
endoderm nuclei of the gastrula stage is so very unlike that of 
the ectoderm nuclei. Compare Pl. XIV, figs. 24—26. 
Before leaving this subject, I may call attention to the small 
bodies present in the endoderm masses in the early gastrula 
stage (fig. 20). These bodies do not stain so deeply as the 
endodermal nuclei, which are now present in small numbers, 
or as the small, deeply-staining bodies seen in the sections of 
the disco-gastrula stage (Pl. XIII, fig. 16); but they stain 
more deeply than the ordinary protoplasmic reticulum. Can 
these bodies have anything to do with the endodermal nuclei 
which are now appearing ? 
This subject is one of extreme interest, and I shall return 
to a consideration of it when I have described the structure 
of the nucleus of the unsegmented ovum and its immediate 
descendants. 
3. The third point of interest in the development of the 
gastrula is the mode of origin of the cavity of the gastrula. 
The solid gastrula consists of a multi-nucleated, much- 
vacuolated mass of protoplasm. The gut of the gastrula 
arises from an enlargement and confluence of the 
