OLIGOCH^TA. 259 



the female organs, and a portion of the course of the vas deferens. 

 The location of the various organs was definitely determined in the 

 entire specimen, and I was able to confirm this in the sections ; the 

 characters of the spermathecse and their ducts, and the fact of the 

 entry of the vas deferens into the proximal end of the atrium, were 

 also made out by both methods. 



Of the four species of Hesperodrilus recorded by Beddard (1, 2) 

 from South America (where alone, so far, the genus has been found), 

 two {H. albussbudH. pellucidus) showed the same form of " cephali- 

 zation " which occurs commonly among the Naididae, that is, the 

 dorsal setae began at a level posterior to the beginning of the ventral 

 setae. The present species shows the same pecuHarity, the dorsal 

 setae beginning in the third, the ventral as usual in the second 

 segment. It is immediately distinguished, however, from both 

 H. albus and H. pellucidus by the much shorter prostomium and the 

 ventral position of the spermathecal apertures. 



The present species displays, in addition, a number of other 

 pecuHarities, which, though striking, have possibly not the same 

 morphological value. Thus the atrium is in segment XIII. instead 

 of XII., and the spermathecal apertures in the posterior part 

 of XIV. instead of in XIII. ; in other words, while in the genus 

 Hesperodrilus as a whole the genital organs are displaped one 

 segment backwards as compared with most Tubificidae, in the 

 present specimen the posterior half of the genital organs show a 

 backward displacement of two segments. 



Among the specimens of H. albus examined by Beddard was one 

 which showed the genital organs in the usual Tubificid position, i.e., 

 displaced one segment forwards as compared with the rest of the 

 genus. Since therefore the position of the genital organs is variable 

 in at least one species of Hesperodrilus, it may be so in the present 

 case also, and it is possible that the peculiar disposition here recorded 

 is merely an individual variation. 



My failure to detect the female apparatus may have been due to 

 the fact that the specimen was only in an early stage of sexual 

 development ; and the absence of sperm-sacs may perhaps also be 

 due to the same cause. It is however unlikely that the entry of 

 the vas deferens into the proximal portion (instead of the distal, 

 as in other species of Hesperodrilus) of the atrium can be similarly 

 explained. 



The following diagnosis, I believe, omits all doubtful points, of 

 both the kinds exempHfied above : — 



Hesperodrilus zeylanicus, sp. no v. Length 8 mm., breadth 

 •6 mm., segments 34 ; prostomium about the length of an ordinary 

 body-segment ; cHtellum 1/5 XII. -XIII. = 1 1/5. Dorsal setae 

 begin in III., up to 5 per bundle, capilliform, longest equal to 

 diameter of body. Ventral setae in pairs of one forked and one 

 singly pointed seta ; one, or occasionally two, such pairs on each 



2 M 6(7)12 



