DEVELOPMENT OP THE CAPE SPECIES OF PEEIPATUS. 539 



soon acquire a dorsal extension, and the cavity in each of them 

 becomes divided into two parts — a ventral part which passes 

 into the appendage, and a dorsal part which comes into contact 

 but does not unite with its fellow of the opposite side on the 

 dorsal wall of the enteron. 



The dorsal portions of the somites early become obliterated 

 in the anterior part of the body, but posteriorly they persist, 

 and those of the same side unite with each other so as to form 

 two tubes which are the generative glands. 



The ventral or appendicular portions persist and retain their 

 original isolation throughout life. They give rise to two 

 structures : 



(1) To a coiled tube, which acquires an external opening 

 through the ventral body wall at the base of the appendage 

 and constitutes the nephridium of the adult ; 



(2) To a small vesicle, which is contained in the appendage 

 and constitutes the internal blind end of the tubular or nephri- 

 dial portion of the somite. (The opening of the nephridium 

 into the vesicle is funnel shaped, and is commonly known as 

 the internal funnel-shaped opening of the former.) 



From the above account it follows (1) that the coelom of the 

 embryo of Peripatus capensis gives rise to the nephridia 

 and generative glands, but to no part of the body cavity of the 

 adult ; (2) that the nephridia of the adult do not open into the 

 body cavity. 



The body cavity of the adult consists, as is well known, of 

 four divisions : — (a) the central compartment containing the 

 intestine and generative organs, (b) the pericardial cavity, 

 (c) the lateral compartments containing the nerve-cords and 

 salivary glands, and (d) the portion in the appendage. 



Of these, without going into details, it may be said that a 

 arises as a space between the ectoderm and the endoderm, b, c, 

 and d as spaces in the thickened somatic walls of the somites. 

 The spaces are in communication with each other. 



The heart arises as a part of a which becomes separated 

 from the rest. Posteriorly it acquires paired openings into 

 the pericardium. It thus appears that the heart and various 



