22 LILIAN SHELDON. 
species of Peripatus, since the germinal spot disappears before 
the germinal vesicle. 
Stuhlmann suggests that the disappearance may have some 
connection with the presence of yolk in the egg, since he has 
observed it in all insect eggs in which yolk is present in large 
quantities, but not in Aphides and Cecidomya, in which yolk 
is absent. Its disappearance in Peripatus capensis, how- 
ever, in which no yolk is present, goes against this theory, 
unless it is to be regarded as a survival from the time when yolk 
was present in the ovum. On the other hand, it is supported 
by the observations of Will (20) and Scharff (13), who state 
that some of the yolk is derived from the germinal vesicle, 
and by the phenomena which I have described in P. nove- 
zealandiz; but these points will be discussed later under 
the Formation of the Yolk. 
Stuhlmann (17) has not observed the disappearance of the 
germinal vesicle in P. Edwardsii, but this may be due to the 
incompleteness of his researches in this species. 
The double disappearance of the germinal vesicle in P. nove- 
zealandiz is, so far as I know, unparalleled, and I am unable 
to offer any explanation of it. The first disappearance seems 
to be that which is homologous with that which commonly 
occurs in ova, and its mode of disappearance will be discussed 
later on. The details of the second disappearance are quite 
unknown, and at first sight it would appear that the nucleus 
shown in the ovum in fig. 30 was the first segmentation 
nucleus; but that this is not the case seems certain from the 
fact that a large proportion of the unsegmented ova which were 
found in the uterus were without any nucleus, and it is not 
easy to conclude that this condition was abnormal since the 
ova were found in several different parents, and were preserved 
in several ways. The only case in which, so far as I know, a 
double disappearance has been described, is that of Millepora, 
in which Mr. Hickson (11) states that the nucleus is dispersed 
before and after the formation of the polar bodies ; but since 
in P. nove-zealandiz I have observed no polar bodies, it 
is not possible to compare the two cases. 
