120 BULLETIN OF THE 
than the disintegration of the nucleus, until the process of gastrulation 
is completed. Such cases are not as common, however, as others, where 
there is to be found ‘in the cleavage cavity material which appears as 
though it had resulted from the disintegration of similar cells. This 
material has a spongy or vacuolated appearance, and contains faintly 
staining bodies or granules similar to those found in the ectodermic 
cells; it does not possess definitely circumscribed boundaries; on the 
contrary, it fills the cleavage cavity more or less completely, but is not 
of uniform density throughout. The fact that this material is not homo- 
geneous, and that it contains granules, etc., prevents the conclusion that 
it has been produced as a simple secretion into the cleavage cavity, 
although it may have been formed in part by such a process. The fre- 
quent association of this material with ingression cells in the same spe- 
cimen (Plate II. Fig. 8), and the lack of other ways of accounting for 
its presence, lead me to believe that it is produced by the disintegration 
which I have suggested. 
There is another peculiarity of the development which I believe to 
be connected with this process of nuclear disintegration. It is this: 
after having once entered the cleavage cavity the immigrating cells seem 
to lose their power of division, and consequently do not become more 
numerous, while the cells composing the blastospheric wall undergo 
repeated divisions, as is shown by their increased number and dimin- 
ished size. 
The number of these immigrating cells is small, usually only one or 
two, very rarely more than three, so that I hav®not been successful in 
finding the “ Verbindungsglieder” connecting the conditions shown by 
Goette (87, Taf. I.) in his Figures 5 and 6, which Claus (90, p. 4) re- 
garded as essential to the substantiation of Goette’s view of the method 
f gastrulation. 
Reference has been made to the fact that in some cases the ingrowing 
cells persist both during and after the process of invagination. In the 
latter case, they are to be found in the celenteron rather than in the 
cleavage cavity. Figure 11 (Plate II.) is drawn from such a specimen. 
Figures 9 and 10 represent two sections of one individual in which the 
invagination is not completed, and furnish a hint as to the process by 
which the cells pass into the cwlenteron from the cleavage cavity. The 
entoderm being composed of less closely fitting cells than the ectoderm, 
doubtless admits the passage of the large immigrated cells through it 
more readily than the latter would (Plate II. Fig. 9). The immigrated 
cell is of course passive in this process. Since it is prevented by the 
