332 WHEELER. PV OL. TIT, 
chromatin, formerly numerous, agglomerate to form one or two 
large irregular masses which usually apply themselves to the 
wall of the clearly vesicular nucleus (Fig. 88 ¢). The wall of 
the nucleus then ceases to be evenly spherical, and becomes 
irregular apparently because the karyochylema is escaping 
through a rent (Fig. 880). In the last stages seen the masses 
of chromatin lie between the yolk bodies, all the other portions 
of the nucleus having disappeared. They still take the char- 
acteristic deep red stain, but finally become comminuted and 
disappear in the intervitelline protoplasm. 
The dissolution of these nuclei and their migration into the 
yolk is brought to a close soon after the entodermic mass begins 
to grow forward. 
The oral mass of proliferating cells is essentially the same as 
the caudal mass just described; but being smaller, I have not 
seen fit to represent it in the plates by enlarged figures. Some 
of the entoderm nuclei degenerate in exactly the same manner 
as those described in the caudal thickening, but the whole mass 
of cells being smaller, the number of these evanescent nuclei is 
much less. 
I am at a loss to assign a meaning to this migration of de- 
generating entoderm nuclei into the yolk unless it be supposed 
that originally all the nuclei of the egg went to the surface and 
that a portion of the entoderm passed into the yolk to form vitel- 
lophags while another portion proliferated forward in compact 
sheets to form the walls of the mesenteron. Later, when the 
ontogeny was abbreviated in the blastoderm stage by cells being 
left in the yolk, this migration of entoderm cells became unnec- 
essary, as the yolk, which is already segmented, is copiously sup- 
plied with vitellophags. The lack of distinct yolk segmentation 
just beneath the two proliferating points may lend some proba- 
bility to this view. I am aware that my explanation halts, but 
it will have to stand, for the want of a better one, till more facts 
are forthcoming on these degenerating nuclei in other forms. 
In examining the literature the only observation which I can 
find similar to the one just recorded is in Hatschek’s paper on 
Bombyx chrysorrhea (18). He observed a mass of nuclei, which 
in his figures have all the appearance of undergoing degenera- 
tion, just anterior to the large mass of entoderm cells attached 
to the oral ectoderm. This mass of nuclei, designated by him 
as a “gland,” soon disappears in the yolk. 
