296 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. novae- 

 zealandise; 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. novse- 

 zealandise 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. novse-zealandise I have observed no polar bodies, it 

 is not possible to compare the two cases. 



