DESCRIPTIONS OF GENERA AND SPECIES 



599 



Spermathecal sacs paired, reacMng back to the seventeenth segment, opening 

 in front into the thirteenth segment. No penial setae. 



This genus was first investigated by Michaelsen (12); subsequently I added 

 (54) a few particulars to what was known of its structure through Michaelsen's 

 researches. 



Nemertodrilus is the only other genus besides Eudrilus and Pareudrilus in 

 which the genital pores, both male and female, are paired. On this account it is 

 excluded by Michaelsen from the subfamily Teleudrilini. 



The reproductive organs are evidently somewhat degenerate as compared with 

 those of other Eudrilids. There are two large sacs, which clearly correspond to the 

 spermathecal sacs of other genera ; these lie on either side of the gut ; they commence 

 at the septum xiii/xiv, and open freely into the cavity of segment xiii. On the 

 other hand they reach back as far as the seventeenth segment. Anteriorly the 

 lumen of these sacs is divided up by trabeculae into numerous chambers, which 

 lodge the developing ova ; this region of the sacs appears to represent the receptaculum 

 ovorum of other Eudrilidae; but it is not sharply marked off from the rest of the 

 sac; there is no break between the two regions. 



Tlieae sacs have been variously interpreted; Michaelsen has suggested, on the one hand, that 

 they represent the greater portion of the spermatheca which has got cut off from the duct ; this on 

 account of the fact that they were found to contain sperm. ' Perhaps, however,' says Dr. Michaelsen, 

 'it would be more correct to consider that the spermathecae are reduced to the smallest rudiment 

 of the duct, and that the sacs are nothing else than a pair of receptacula ovorum which have also 

 taken on themselves the function of spermathecae.' My own discovery, confirmed by Rosa, that the 

 so-called spermathecae of the Eudrilidae are merely coelomio pouches formed at the expense of 

 the septa, seems to strengthen the first-mentioned view, with which I agree. 



The ovaries are in the thirteenth segment afiixed, as usual, to the front wall of 

 that segment ; the cavity of the segment is greatly reduced so that the ovaries get 

 to be very near the open mouth of the sac already described ; there is thus no 

 need for any special investing sac for the ovaries. Into the cavity of this segment 

 also open a pair of pores referred to in the generic definition; the orifices are 

 fringed on the internal side with a number of frayed out cellular processes of the 

 peritoneal epithelium; this arrangement permits of the entry of bodies from without, 

 but hinders the exit of spermatozoa from within. Michaelsen pointed out that 

 these paired orifices are the external apertures of the spermathecal sacs ; it appeared 

 to me that they might be the rudiments of ■ a second pair of oviducts ; I am now 

 convinced that Michaelsen's interpretation is the right one. Now that we know 

 that the spermathecae of the Eudrilidae are coelomic sacs, not comparable, morpho- 



