142 CHANGES FROM STAGE G TO BIRTH. 



ducts. In the male the tubes are considerably twisted ; 1 could 

 not make out any distinct trace of the vesicula seminalis. 



I regret to say that I have not paid much attention to the 

 histological development of the sexual glands. The first trace 

 of the sexual organs is the round nuclei of the endoderm'. 

 When and how these acquire a cell body I cannot say. They 

 certainly have the latter by Stage g (PL IX, figs. 47, 48). 

 The follicular nuclei are the nuclei of the splanchnic meso- 

 derm, which closely apply themselves to the germinal nuclei as 

 soon as the latter emerge from the endoderm. The follicular 

 nuclei appear, therefore, before the protoplasm of the sexual 

 cells (PI. VII, fig. 26). In Stage g areas of protoplasm, in- 

 distinctly marked off from one another, could be distinguished 

 round the larger nuclei (PI. IX, figs. 47, 48). In the 

 females of the stage just before birth the boundaries of these 

 areas were slightly more marked, but still indistinct (PI. 

 XI, fig. 12). In the male of this stage there are no lines 

 separating the protoplaem round the granular nuclei of the 

 testes into areas (PI. XII, fig. 13). 



The general bearing of the facts of development of the 

 coelom and body cavity of Peripatus is fully dwelt upon in 

 Ch. V, p. 116. I have but little doubt that the same method 

 of development will be found in other Arthropoda. If I am 

 right in this view it must be admitted that the Arthropoda 

 are coelomate animals, that their generative cells are products 

 of the coelomic epithelium, and that the generative ducts are 

 modified nephridia. 



The coelom of Peripatus does not extend into a perivisceral 

 or body cavity, but remains small, discharging only the func- 

 tions of excretion and reproduction. The functions of a peri- 

 visceral cavity are discharged by the vascular system, in which 

 indeed the coelom is contained (PI. XI, figs. 10, 11, 13, 

 and diagram, fig. 17) in exactly the same way as the intestine 

 of a mammal is contained in the coelomic body cavity. The 



