AN ATTEMPT TO CLASSIFY EAETHWORMS. 237 



Remarks on the Perichsetidge. 



Although some fifty species of this genus have been formed 

 within the last few years (besides those which have been cha- 

 racterised only by their external anatomy^ and which must be 

 in many cases discarded), yet very frequently insufficient data 

 have been given. On the whole it is a Well-defined family, but 

 the single genus may really be capable of subdivision. 



I have already mentioned my reason for removing Peri onyx 

 from the family, a proceeding which may at first appear 

 arbitrary. 



The character of the prostomium and the presence or absence 

 of the characteristic intestinal caeca, as well as the position of 

 the gizzard, may prove to be of generic value. The observa- 

 tions on the excretory system are in most cases very superficial 

 and incomplete, and frequently no mention is made as to 

 whether in a particular species large " nephridia" or a small 

 network of tubules is present. Where these observations have 

 been carefully made the presence of a pair of large nephridia^ 

 appears to be associated with the absence of the intestinal 

 cseca, a forward position of the gizzard in Somite v or vi, 

 and with the existence of three pairs of spermathecse. But 

 there are too many apparent exceptions to generative on this 

 point at present. 



Amongst the more peculiar species may be mentioned P. 

 indica, Horst, where some of the more ventral setse are larger 

 than the rest; P. hasseltii, Horst, in which the ventral setse 

 are more closely placed; P. stuarti. Bourne, with two pairs 

 of male pores and two pairs of prostates. P. bakeri and 

 P. intermedia have prostates resembling those of Acan- 

 thodrilus. 



The number of setse per somite, position of copulatory 

 papillse, extent of clitellum, number of spermathecse and shape 

 of appendix, and of the prostates, serve as the leading characters 

 in which the species differ from one another. 



The worms figured by Schmarda are only described so far 

 1 Probably accompanied by a network. 



