402 EARLIEST STAGES OF THE DEVELOPMENT OF ANIMALS 
iS) 
. According to Bischoff, Kolliker, and the majority of embryolo- 
gists, the germinal vesicle and its contents disappear, and have no 
direct connection with the cells of the blastoderm. 
3. According to observations of the late Johannes Miller, of 
Gegenbaur and others, the germinal vesicle may give rise directly, by 
division, to the cells of the blastoderm. 
The study of the development of the embryo of Pyrosoma yields 
results in close conformity with the last view. The ovum of this 
animal is, in fact, composed, at first, like all others, of germinal vesicle, 
germinal spot, and vitellus; but, in the course of development, 
the vitellus disappears, probably becoming liquefied, and the germinal 
vesicle is laid bare, so that it becomes comparatively easy to watch 
the subsequent changes in its interior. These consist in the deposit 
of a somewhat opaque matter and the division of the germinal spot, 
so as to give rise to the endoplasts, or “ nuclei” of the blastoderm, 
which is thus primarily formed within the interior of the germinal 
vesicle, 
The speaker concluded by observing, that it is not improbable 
that the process thus traced, is similar to that by which the blastoderm 
of the higher Alzzzlosa arises, and that it will probably furnish 
the key to the signification of the multiple germinal spots observed in 
so many of the lower Vertebrata; while, by proving the direct descent 
of some of the histological elements of the progeny from those of the 
parent, it combines the theories of the pre-existence of germs with 
that of epigenesis. 
