64 RICHARD EVANS. 



and thirdly, the generative ducts develop almost exclu- 

 sively from the ectoderm by invagination (4). 



According to Mr. Sedgwick's description, first, the germinal 

 nuclei arise from the endoderm, and only later acquire a 

 relation to the mesoderm ; secondly, several pairs of somites 

 take part in the formation of the generative organs; and 

 thirdly, the generative ducts are derived from the appendi- 

 cular outgrowths of the somites of the anal papillte (5). 



The Germinal Nuclei and their Place of Origin. — 

 Having made a brief statement of the present position of 

 our knowledge of the development of the generative organs 

 of the Peripatidae, I shall proceed to give an account of 

 their origin and growth in the genus Eoperipatus. It 

 would seem that the germinal nuclei can be distinguished at 

 an earlier stage in the prospective female than in the male; 

 for this reason the following description applies to the 

 former rather than to the latter. Because the number of 

 metameres present in the body is not constant, it will be 

 necessary to refer to the somites as counted from the 

 posterior end, though in the early stages this method has 

 the disadvantage that the generative nuclei appear before 

 the last two somites are formed. The somite of the genera- 

 tive duct is the third from the posterior end, som,"''^, the 

 somites in front of it being som."'^, som."''^, etc. 



Each of the embryos, sections of which are represented in 

 figs. 13 and 14 on Pi. 8, possessed twenty-five pairs of 

 somites, that is two pairs fewer than the smaller number 

 that are accounted for in the adult female. Consequently 

 the last actually developed pair of somites in the two 

 embryos under consideration must be labelled som."'^, and 

 the pair situated immediately in front of the last one, and 

 shown in section in the two figures above mentioned, as 

 som."'^. In the two embryos represented in section in these 

 figures, germinal nuclei occur in the splanchnic walls of 

 four pairs of somites situated immediately in front of the 

 last actually developed pair {som."'^), but they are more 

 numerous in the twenty-third and twenty-fourth pnirs than 



