DEVELOPMENT OP THE CAPE SPECIES OF PERIPATUS. 391 



condition of the coelom and vascular tracts in the adult and 

 the relation of the coelom to the vascular body cavity is clearly 

 illustrated by the diagram (PL XXIX, fig. 17). It is commonly 

 said that in the Arthropoda the generative ducts are continu- 

 ous with the glands, and in this they are contrasted with the 

 Annelida and Vertebrata. As a matter of fact, however, the 

 generative ducts, in Peripatus at least, present exactly the 

 same relation to the generative glands as do the oviducts of a 

 dogfish or earthworm to the ovaries of these animals ; that 

 is to say, like the latter, the generative ducts open into the 

 ccelom, and the ova are products of the ccelomic epithelium. 



It is important to notice that in Peripatus the nephridia 

 are parts of the coelom (PI. XXIX, diagram, fig. 17), just as 

 they are in Elasmobranchs. They are commonly spoken of in 

 a manner which implies that they have but little to do with 

 the coelom beyond opening into it. This way of speaking 

 of them is calculated to mislead. The nephridia are 

 direct differentiations of part of the ccelom (dia- 

 grams, figs. 13 — 17, and figures in Part III illustrating their 

 development). 



A negative feature, which has often been put forward as 

 characteristic of the Arthropoda, is the apparent absence of 

 nephridia. The nephridia of Peripatus have generally been 

 considered as a primitive and peculiar feature. Lankester, 1 

 however, some time ago (No. 54, p. 516), suggested that the 

 coxal glands of Limulus and the antennary glands of Crus- 

 tacea were nephridia, and that the peculiar "end-sacs" 

 described by Gulland in the coxal glands of the young 

 Limulus, and the internal vesicle of the Crustacean anten- 



1 Lankester's words were : " The observations here recorded oil the struc- 

 ture and connections of the immature coxal gland of Limulus tend to render 

 it probable that the green glands of Crustacea are also to be regarded as a 

 pair of modified nephridia;" and he goes on to say that "it seems not 

 improbable that the so-called end-sac of these glands is not part of the 

 nephridium, but is developed from the connective-tissue space (coelomic space) 

 into which the true tubular nephridium opens." The distinction implied by 

 these last-quoted words between the nephridium and coelom is not justified 

 by embryology, as I have just pointed out. 



