534 ADAM SEDGWICK. 



or less well-marked cavity are formed in the embryo ; but the 

 fate of these structures has never been followed. We do not 

 know whether their cavities enlarge and unite with one another 

 and give rise to the body cavity and vascular system of the 

 adult, or whether they shrivel up and disappear, their walls 

 only remaining as part of the mesoderm. From what has 

 been said it is also clear that it is impossible to say whether in 

 the Arthropoda the vascular system is nipped off from the 

 coelom, or whether it arises as a separate set of spaces in the 

 mesoderm, as in Annelids and Vertebrates. 



Now, Peripatus is a true Arthropod so far as its body 

 cavity is concerned : thus the heart drives the blood into 

 it, and by means of the paired cardiac ostia sucks the blood 

 out of it ; it does not communicate with the exterior by nephri- 

 dial pores, nor does its lining develope generative cells. We 

 are therefore justified in regarding the body cavity of Peripatus 

 as homologous with that of other Arthropoda. It results 

 from this that the study of the development of the body 

 cavity in Peripatus, which can be traced with comparative 

 ease, must be of extreme interest, as tending to clear up the 

 question of its ccelomic or non-coelomic nature in Arthropoda 

 generally. 



Kennel was the first to trace the body cavity of Peripatus. 

 He showed that it was in part, at any rate, a pseudocoele, but 

 his work was incomplete in that he failed to follow correctly 

 the fate of the coelom. He thought that the coelom became 

 merged into the body cavity. If this were correct, it would 

 follow that in Peripatus the vascular system and coelom would 

 be in communication. 



As has been fully shown in the preceding pages, this is not 

 the case. The coelom of Peripatus can be traced through the 

 whole development, as a system of spaces shut off at all stages 

 of its growth from the system of body-cavity spaces. In the 

 adult Peripatus the coelom is in the following condition : (1) a 

 series of nephridia ending internally in small thin-walled 

 closed vesicles ; (2) two dorsal tubes — the generative glands 

 and the ducts of these, which latter are derived from one pair 



