9 



eloso to the splanchnoplcura. Their lattcr situation iii the splancli- 

 noplcura is a sccondary one: they enter it from without. 



Evans' doscription of the development of the female generative 

 organs of EoperipatHS Weldoni agroes in the main points with 

 that of Sedgwick, with these diflPerences, that the ovaries are 

 built up from only four pairs of somites and that the sexual 

 ccUs are said to arise in the ventral walls of the ovaries itself. 

 I think however, that Sedgwick's figures are very convincing 

 and clearly demonstrate that in the species examined by him the 

 sexual cells, if perhaps not in the entoderm, yet certainly take their 

 origin independently from the walls of the somites. Perhaps in 

 this point there is a difference between the various species. 



DiflFerence of the examined species possibly also explains the 

 discrepant results of Yon Kennel. According to this author the 

 generative organs in the American species examined by him are 

 formed by only one pair of somites, whereas in the preceding 

 segments of the body a complete dissociation of the w^alls of the 

 somites takes place. 



From the observations of Sedgwick and Von Kennel it seems 

 possible to conclude that the coelom of the ancestors of the Ony- 

 chophora must have had a greater extension. By its reduction 

 cells, formerly lying in the wall of the coelom, now come free 

 into the primary body cavity. Among these cells, the „coelenchym" 

 of Salensky '), are the generative cells. The body cavity of Ony- 

 chophora is to be considered as a „mixocoel", arising from 

 the union of the primary and part of the secondary body cavity. 

 By this assumption the falling of the eggs in the body cavity, 

 which in fact is partly a rest of the coelom, becomes easily in- 

 telligible. The cavities of the generative organs and of the nephridia 

 are derived from only a part of the coelom of the ancestors, the 

 Polychaeta. The walls of the remainder of the coelom are oblit- 

 terated, and the sexual cells, originating in them, in the recent 



1) Morphogenetischc Sfciulica an Wiirmern. Mem. Acad. St.-Péiersbourg, (8), 

 Vol. 19, 1907. 



