DEVELOPMENT OF THE OAPE SPECIES OF PERIPATUS. 201 
changes which they undergo. I have not been able to make 
out the sequence of these changes, but I hope with more ma- 
terial, which I expect to obtain this year, to be able to com- 
municate some more facts concerning them in a future paper. 
It is a disputed point as to whether or no the nuclear and 
extra-nuclear reticulum are continuous. Leydig (12), Stricker 
(16), Klein (9, 10,11), and Heitzmann (5), hold that they are. 
So far as the nucleus of the early segmentation stage, and of 
the endoderm of Peripatus is concerned, I am able fully to 
confirm the views of these observers. 
The general views I hold with regard to the nucleus are stated 
on p. 189 and I need not repeat them here. I only desire to 
point out that the opposite view, viz. that the nucleus is iso- 
lated, so far as continuity of protoplasm is concerned, is, from a 
physiological point of view, very difficult to accept ; and I think 
that the burden of proof rests with him who maintains it. 
The peculiar lobed structure (Pl. XII, fig. 3) of certain stages 
of the nucleus has been described before by other observers, 
notably by Balfour in his “ Monograph on the Development of 
Elasmobranch Fishes,” in the early stages of development. 
Klein in his communication on this subject, refers (9, p. 175) 
to and confirms Stricker’s (16) observations on the contractility 
of the nuclear spongework and its continuity with the extra- 
nuclear spongework in the colourless blood-corpuscles of the 
newt and frog. He further confirms Stricker’s statement as to 
the disappearance of the cell membrane, and himself adds: 
“The nucleus is therefore a part of the cell sub- 
stance specially differentiated by the presence ofa 
membrane.” Presumably Dr. Klein would still speak ofa 
nucleus when the membrane isabsent. Iam notable to make 
out Klein’s views with regard to this membrane. He says (11, 
p. 415): “‘ In the convolution and basket of daughter nuclei the 
membrane is very indistinct and is also here due to the close 
position of the fibrils.” I infer from this that he regards the 
nuclear membrane as a part of the general reticulum at the 
junction of the nuclear and extra-nuclear parts of the reticulum, 
which gets in certain stages of the nucleus a regular ar- 
