DEVELOPMENT OP THE CAPE SPECIES OF PERIPATUS. 513 



The Somites of the Twenty-first Pair, or somites of the anal 

 papillae, never become divided into two parts. The median divi- 

 sion remains in connection with the lateral (PI. XXXVII, fig. 44), 

 which, however, as in the case of the other somites, acquires 

 a ventral diverticulum. This hugs the outer side of the nerve- 

 cord, and acquires in late embryos of Stage f an external 

 opening which, however, is much nearer the middle line than 

 in the case of the anterior somites, and, indeed, may be 

 described as being common with that of the opposite side. 

 However this may be, the two openings soon become definitely 

 united to form a single opening, — the generative opening, while 

 the tubes themselves persist as the generative ducts. Whether 

 any large portion of the latter are ectodermal in origin, that is 

 to say, derived from a growth of the lips of the opening at 

 its first appearance, it is impossible to say. Kennel asserts 

 that a large part of the generative duct is so derived, but it is 

 obvious that such a statement, as in the case of the anterior 

 segmental organs, cannot be regarded as anything more than 

 an expression of probability. It is impossible to settle the 

 question by sections, and 1 know of no other method. 



From the above description of the origin of the generative 

 organs and their ducts, which is in the essential points identical 

 with that of my tentative preliminary account (No. 33), it is 

 obvious that Kennel has failed to trace the origin of the 

 germinal nuclei. He also differs from me as to the origin of 

 the generative tubes themselves, which, he asserts, come from 

 the dorsal divisions, not of a series of somites, but of one 

 single pair. If his account is correct, which, seeing that he 

 has not observed the origin of the germinal nuclei, I am 

 inclined to doubt, it would appear that the generative tubes of 

 the Cape species differ from those of the West Indian in this 

 respect. He adopts my account of the derivation of the gene- 

 rative ducts and their openings from the lateral divisions of a 

 pair of somites, though, curiously enough, in another place he 

 stigmatises my description as " falsch." 



It thus appears that in Peripatus capensis the nephridial 

 portion of the twenty-first somite does not separate from the 



