THE ANATOMY AND DEVELOPMENT OF PERIPATUS NOVAE-BRITANNIAE. 31 



the caudal or abdominal region as it increases in length and independence. After 

 the appearance of the cephalic flexure (Stage IX), the trophic organ gradually 

 decreases in relative dimensions until it is finally completely reduced to its definite 

 proportions as part of the body of the animal. 



In its capacity of dorsal trophic organ, the trophoblastic vesicle of the embryos 

 of P. novae-britanniae is therefore comparable with the stalk of the embryo of the 

 Neotropical Peripatus. 



The stalked embryos of P. torquatm and edwurdsii (= trinidadensis) were dis- 

 covered and described by Kennel in 18SG, and the discovery was confirmed by 

 W. L. Sclater (17) in 18.S8. The two authors however differed considerably in their 

 interpretation of their observations. Both agreed that the embryo is attached by a 

 dorsal stalk to the inner wall of a closed vesicle. The embryo therefore lies inside 

 the vesicle as in a brood-chamber. Kennel described the vesicle as being derived 

 from the uterine epithelium which entered into relations with the embryo and rounded 

 off at the ends to form a closed chamber. Sclater described the wall of the vesicle 

 as a pure and simple derivative of the embryonic ectoderm, the cavity of the vesicle 

 being produced by separation of the inner and outer layers of the so-called pseudo- 

 gastrula, as in the Mammalian embryo. The figures given by Kennel and Sclater 

 are remarkably alike, only they differ in their statements as to the relative ages of 

 embryos. On the whole there are fewer gaps and fewer unique phenomena in 

 Sclater's than in Kennel's description. In P. novae-britanniae there is no question 

 as to whether the vesicle is an embryonic or uterine derivative. It is of course an 

 embryonic structure, and the embryo lies outside and upon it, instead of inside it, 

 as in the Neotropical species. Korschelt and Heider (13) summed up in favour 

 of Kennel's interpretation. I think my results rather favour Sclater's conclusions. 



In the embryo of P. novae-britanniae there is normally no space between the 

 egg-membrane and the enclosed embryonic vesicle, but the membrane closely hugs 

 the latter, and no doubt the vesicle in life is turgid and tightly pressed against the 

 uterine wall. The uterine epithelium shows signs of great glandular activity with 

 its vacuolar cells, and its inner surface is often raised up into small prominences 

 caused by the artificial separation of the embryo from contiguity with the wall. The 

 uterine epithelium is locally thickened in the neighbourhood of an embryo. 



In P. capensis Sedgwick states that in normal embryos there is always a space 

 between the embryo and the membrane filled with fluid, and in his Stages E to F 

 the dorsal ectoderm is much thickened and vacuolated, especially in the region of 

 the so-called dorsal hump, and probably, according to Sedgwick, has a nutritive 

 function, absorbing the fluid in which the embryo lies. 



In P. novae- zealandiae the dorsum of the embryo is occupied by yolk ; and 

 Miss Sheldon has described a peripheral layer of yolk or ectodermal yolk between 

 the embryo and the egg-membrane, thus occupying the same position as the nutrient 

 fluid in P. capensis. 



In the Neotropical Peripatus the egg-membrane completely disappears before the 

 close .of the segmentation stages (Kennel 11, Sclater 17), and the embryo becomes 

 applied against the uterine wall without any intervening membrane. In some cases 

 (P. torquatus Kennel) circular ridges are developed on the outer wall of the vesicle 



