I9I7-] J- Stephenson : Indian Oligochaeta. 



359 



THE SYSTEMATIC POSITION AND RELATIONSHIPS OF 

 THE GENUS HOPLOCHAEFELLA. 



That Hoplochaetella. as here defined, is the direct ancestor of 

 Erythraeodrilus seems certain. It happens that Eryihraeodnlus 

 (both batches,— the original specimens collected in 1913, as well as 

 the example in the present collection) and the five species of Hoplo- 

 chaetella here described (though not the type species, Perichaeta 

 stuarti), come from within a few miles of each other, the general 

 facies is similar ; and the two genera agree in such peculiarities as 

 the point where the meganephridia begin, the position and relative 

 sizes of the calcareous glands, the length and disposition of the pros- 

 tatic ducts, the presence of accessory spermathecal glands, and the 

 vascular commissure of segment xiv ; some of these are so special [e.o 

 the accessory spermathecal glands, the vascular commissure in xiv) 

 that they cannot be regarded as other than marks of close affinity. 



The differences are :— the fusion of the septa in the region of 

 the testes in the one, and the presence of testis-sacs of the usual type 

 in the other ; the three pairs of seminal vesicles and the absence of dis- 

 placed setae in the spermathecal region of Erythraeodrilus ; the (some- 

 times, apparently) common opening of the spermathecae of the same 

 side in Erythraeodrilus; and especially,— the essential point,— the 

 total disappearance of the posterior pair of prostates in the 'latter 

 genus. What we have, in fact, in these two genera, is two successive 

 stages in the reduction of the original Acanthodrihne male apparatus. 



This may be illustrated by the figures on page 360. Text-fig. i 

 gives a diagrammatic representation of the primitive condition, as 

 found in Notiodrilus (I use the name in the sense in which it was 

 used, for example, by Michaelsen in his " Geographische Verbrei- 

 tung der OHgochaten ") ; the testes are free in segments x and xi, 

 the vasa deferentia open on xviii, the two prostates independently 

 on xvii and xix, the spermathecae in grooves jl^ and 8/9. In the 

 Megascolecinae the reduction takes place by the union of prostatic 

 and proper male apertures in segment xviii,— in the situation of the 

 opening of the vas deferens (text-fig. 2). In the Octochaetinae 

 however, a different process is at work, which ends in Eutyphoeus 

 in the amalgamation of the opening of the vas deferens with the 

 anterior prostatic pore in xvii, and disappearance of the posterior 

 prostates ; at the same time the two pairs of spermathecae are re- 

 duced to one, and similarly the two pairs of testes (text-fig. 5). The 

 concomitant reduction of the prostatic and spermathecal apertures 

 is related to the fact that the prostatic apertures of one worm are 

 apposed in copulation to the spermathecal apertures of another. 



In Hoplochaetella we have the condition shown in text-fig. 3. 

 The opening of the vas deferens has fused with that of the ante'rior 

 prostate ; the prostatic apertures themselves seem previously to 

 have approached closer together, since they are found, not on the 

 middle of segments xvii and xix, but in or almost in the grooves 

 17/18 and 18/19, — almost as if the first impulse was to follow the. 

 .Alegascolecine mode of reduction. But (if I may continue to use 



