SUMMARY. 128 



large amount of food yolk present in the embryos, and there 

 is not, at present, any completely satisfactory history of it. 



The development of Peripatus capensis, which is a true 

 Arthropod, so far as its body cavity and vascular system are 

 concerned, is comparatively easy to follow. 



The coelom appears in the ordinary manner as a series of 

 cavities, one in each mesoblastic somite. 



The somites, which are at first ventro-lateral in position, 

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

 becomes divided into two parts — a ventral part which passes 

 iuto 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 append- 

 age and constitutes the internal blind end of the tubular 

 or nephridial portion of the somite. (The opening of the 

 nephridium into the vesicle is funnel shaped, and is com- 

 monly 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. 



