30 THE ANATOMY AND DEVELOPMENT OF PERIPATUS NOVAE-BRITANNIAE. 



The cuticle which occurs during Stage XI over the free surface of the gastral 

 epithelium is a definite membranous exuvia and not merely a condensation of the peri- 

 pheral protoplasm (see Text-figure 6). 



My observations on the endoderm of P. novae-britanniae may be briefly summarised 

 as follows : 



1. In Stage VIII many endoderm cells forsake their epithelial position and become 

 converted into wandering trophocytes. 



2. In Stage X the endoderm commences to reconstitute itself. The trophocytes 

 tend to become less numerous, either being absorbed or applying themselves to the basal 

 membrane, which has been secreted by the endoderm cells concomitantly with the separation 

 of the inner and outer germ-layers to form the definite body-cavity. The endoderm may 

 be said to contract away from the ectoderm. 



3. In Stage XI the endoderm cells have increased in height and secreted a cuticular 

 membrane, and now constitute a fairly compact epithelial layer containing numerous 

 eosinophile globules of varying sizes. The proctodoeum does not yet open into the gastral 

 cavity. 



4. In Stage XII the endoderm commences to undergo histolytic changes, the 

 cuticle ruptures and the globules tend to loosely fill up the gastral cavity. The proc- 

 todoeum now opens into the latter. 



5. In young individuals the brightly staining globules have entirely disappeared. 

 The endoderm does not form an epithelial layer, but consists of cells lying loosely and 

 freely in the gastral cavity like the trophocytes in the embryo. Faintly staining minute 

 spherules may be present. 



The production of trophocytes may be looked upon as a partial histolysis, so that 

 one histolytic change with subsequent reconstitution of the endoderm is at least an 

 observed fact. Then appear the yolk-like globules in the endoderm, and then comes a 

 second histolysis. These are also observed facts. What I have not observed is the 

 reconstitution of the endoderm after this second histolysis. The reconstitution might not 

 occur— assuming that it would occur — till months after birth. To definitely establish the 

 existence of a periodic phenomenon, such as I suppose this histolysis of the endoderm to 

 be, periodic observations are required, and these are at present lacking, with no immediate 

 prospect of the want being met, and this must be my excuse for the imperfection of the 

 above remarks. 



Nutrition of the Embryo. 



It is quite clear that the nutrition of the embryo is effected through the walls 

 of the trophic organ or vesicle and that the ectoderm of the vesicle is physiologically 

 comparable with — perhaps its function is identical with — the peripheral ectoderm or 

 trophoblast (Hubrecht) of the Mammalian blastodermic vesicle. 



The trophic organ occupies at first the entire dorsum of the embryo, beyond 

 which it projects freely in front as the head-fold, and behind as the tail-fold. As 

 growth proceeds the caudal or growing end of the embryo emancipates itself from 

 the wall of the vesicle, although the cavity of the latter is directly continued into 



