162 FRANK E. BEDDAED. 



beside another seta, may represent only setae ready to replace 

 the others ; but as they were perfectly mature, and appeared to 

 protrude from the body, it is at least equally possible that this 

 segment was furnished with two pairs of setse in addition to 

 seven scattered setse. I did not observe anywhere else more 

 than eight setae in the segment, though their arrangement in 

 two ill-defined rings was very noticeable on several of the 

 anterior segments. In Perichseta Houlleti I have occa- 

 sionally seen a similar dislocation of the ring of setse, but in no 

 other forms, though I have not yet specially investigated the 

 point. These various facts with regard to the setae have some 

 bearing upon, though of course I do not pretend that they 

 entirely explain, an important question in Annelid mor- 

 phology. 



One of the most remarkable facts in the structure of this 

 group is the varying position of the different organs in 

 different genera and families. For example, in most earth- 

 worms the testes are in x, xi, and the ovaries in xiii ; in 

 Nais, on the other hand, the testes and ovaries are respec- 

 tively developed in the vtli and vith segments. Are we to con- 

 sider in such cases that the testes of one form are perfectly 

 homologous with the testes of another genus which are placed 

 in a different segment ? or are we rather to regard them as 

 ' serially homologous,' believing that any and every segment 

 can develop testes, which are actually developed here in one 

 case and there in another? A third possible alternative is to 

 consider that Nais and Lumbricus have been evolved along 

 different lines from a common ancestor, in which there were at 

 least six pairs of testes, occuping Segments v, vi, vii, viii, ix, 

 X, XI. If either of these views were true, we might expect to 

 meet with abnormal specimens with a larger number of testes; 

 but this is not the case — such individuals have not been met 

 with.^ Connected with this view as to the reason for the 



1 It is true that Lumbricus is often provided with what appear to be au 

 additional rudimentary pair of ovaries in Segment xii. But this is hardly a 

 case in point, inasmuch as the normal presence of the ovaries in Phrcoryctes 

 and Eudrilus seems to indidate, as do other considerations, that two ovaries 



