jgiy.] J. Stephenson : Indian Oligochaela. 361 



such expressions) when the prostatic pores reached this position, the 

 ending of the vas deferens was able to jump the interval, and 

 united itself with the prostatic pore in furrow 17/18. 



The next stage is Erythraeodrilus (text- fig. 4). Union between 

 the end of the vas deferens and the anterior prostatic pores having 

 been accomplished, the posterior prostates suddenly disappear. 

 Two pairs of spermathecal openings are now superfluous, and the 

 ducts of the spermathecae of the same side approach each other ; 

 various stages of this are met with in the several specimens of 

 Erythraeodrilus kinneari that have been studied {v. post.) ; in one, 

 the two ducts of the same side appear to open practically at the 

 same spot, on the middle of segment viii. We may suppose that 

 the course of evolution is leading, first to the union of the sperma- 

 thecal apertures, then to the disappearance of one spermatheca 

 on each side ; then (if we may take a clue from Eutyphoeus) the re- 

 maining prostatic apertures will advance again to their original 

 position on the middle of segment xvii, and the now single sper- 

 mathecal apertures to their original position on furrow 7/8. 



I need scarcely guard myself from misconstruction by saying 

 that Hopiochaetella and Erythraeodrilus are not, of course, in the 

 ancestral line of Eutyphoeus at all, since Eutyphoeus retains the 

 primitive paired setae. But the same change which has led to 

 Eutyphoeus appears to be going on in a parallel line of forms with 

 the perichaetine setal arrangement. 



Erythraeodrilus being thus the descendant, can we particular- 

 ize regarding the immediate ancestors of Hopiochaetella ? In a 

 previous paper (19) I supposed Erythraeodrilus to be a descendant 

 of Howascolex (which has lumbricine setae, acanthodriline male 

 organs and mixed mega- and micronephridia) by a process of 

 microscolecine reduction of the male organs and perichaetine 

 increase of setae. Hopiochaetella would thus show us the stage in 

 which increase of setae has taken place, but not as yet the micro- 

 scolecine reduction ; this is however being prepared for, since the 

 male ducts already open in common with the anterior prostates ; 

 thus Hopiochaetella would be intermediate between Howascolex and 

 Erythraeodrilus. There is perhaps'some little difficulty with regard 

 to the nephridial system. It is true it is of a mixed nature, — 

 meganephridia and micronephridia co-existing, — in both. But 

 while in Hopiochaetella and Erythraeodrilus micronephridia ' exist 

 throughout the body, and meganephridia only from segment xx 

 onwards, in Howascolex meganephridia exist throughout, and micro- 

 nephridia only make their appearance behind the anterior region , 

 in the middle portion of the body. I do not, however, think that 

 we yet know enough of the exact way in which the change from 

 mega- to micronephridia has taken place (it has quite possibly 

 taken place in more than one way) to enable us to say that this 

 difference prevents our deriving the one from the other ; the con- 

 dition in Howascolex is at any rate apparently less modified than 

 that in Hopiochaetella and Erythraeodrilus. 



There is another possibility as regards the derivation of Hoplo- 



