ON THE OCELOM, GENITAL DUOTS, AND NEPHRIDIA. 497 



funnel is formed as an outgrowth, which fuses with the epidermis 

 (figs. 15 and 16). V. Kennel maintains that in Peripatus 

 Edwardsii the mesoblastic funnel is met by an epiblastic 

 invagination, and the question arises as to whether this 

 invagination represents a true nephridium, in which case the 

 segmental organ of Peripatus would be a compound organ 

 similar to that of Psygmobranchus (see above), or whether it 

 is merely a secondary invagination of the epidermis, such as 

 occurs more or less pronounced in almost every case where a 

 tube opens on to its surface (vesicle of the nephridia in the 

 Hirudinea, peripheral end of the genital ducts of the Oligo- 

 chaeta, &c.). I am inclined to take the latter view, and con- 

 sider the segmental organs of Peripatus as purely peritoneal 

 funnels which have assumed the excretory functions. Whilst 

 these organs have developed in this way, the dorsal or genital 

 halves of the somites in the posterior segments have become 

 fused, forming two genital tubes communicating posteriorly 

 with the undivided coelomic follicles of the last segment. The 

 peritoneal funnels of this segment retain their primitive func- 

 tion, and develop into the genital ducts (fig. 17). The peri- 

 pheral ends and median portion of the ducts are probably 

 derived from the epidermis. 



The history of the genital and excretory organs of the other 

 groups of Arthropoda can easily be brought into agreement 

 with the development of these parts in Peripatus. However, 

 whereas in the latter all the coelomic follicles give off peritoneal 

 funnels, in the Crustacea, Arachnida, Myriapoda, and Hexa- 

 poda the peritoneal funnels are only fully developed in a very 

 few segments. The shell glands and green glands of the 

 Crustacea have been shown to bear the relations of peritoneal 

 funnels (Grobben, 45; Weldon, 104; Marchall, 77; Allen, 1) 

 and develop from the ccelomic follicles. " Bei Daphnia,^' says 

 Lebedinsky (73), "entwickeltsich . . . die Schalendriise als die 

 Ausstiilpung der Somatopleura, welche sich zur Max.^ richtet 

 und hier sich mit dem Ectoderm vereinigt." The same author 

 describes the development of the coxal gland of Phalangium as 

 a typical peritoneal funnel derived from a coelomic follicle (73), 



