48 THE LEECHES - OF MINNESOTA 



From each testis there arises, usually from the inner ventral 

 margin, a vas deferens, (vd. Figs. 4, PL C, 11 and 12, PI. D). The 

 place of origin of the vas deferens with respect to the testis is not 

 constant as it may sometimes arise even from the outer margin, as 

 in the fifth testis of the left side, (Figs. 4 and 11). After leaving 

 the testis the vas deferens arches dorsally and outward, finally unit- 

 ing with the vas deferens communis (vdc) for that side. The vas 

 deferens communis takes its origin in the vas deferens of the sixth 

 testis, running dorsad and cephalad, dipping slightly to receive the 

 vas deferens from each testis. After passing into somite XIII it 

 bends vetrad and medially. In somite XII it turns sharply dorsad, 

 then cephalad and ventrad ; then comes a more or less complete 

 loop which joins the larger vesicula seminalis, (vs, Figs. 11, 12 and 

 13, PI. D). The vesicula seminalis arches dorsad, cephalad and 

 ventrad, then again turning cephalad becomes continuous with the 

 smaller ductus ejaculatorius, (d, Figs. 11, 12, 13 and 14, PI. D) at 

 about XI/XII. The ductus ejaculatorius winds about in somite 

 XI with several loops and at the front of the somite becomes 

 greatly enlarged into the end portion(s) which Whitman, '91, has 

 shown, in Clepsinc plana, to secrete the spermatophore. This en- 

 larged portion arches dorsad, caudad, and ventrad, and then turns 

 to the median line where it joins the similar duct from the opposite 

 side in a common atrium (a. Fig. 15 and Figs. 13 and 14, PI. D). 

 This common cavity opens, by a narrow passage with thick muscu- 

 lar walls, into the enlarged bursa (b) which connects with the out- 

 side by means of the male genital pore. 



The course of the genital duct is very nearly constant in differ- 

 ent individuals and is often an important factor in determining 

 species. Barrows, '93, referring to this fact, said, "It is found that 

 in two species of Aulostoma . . . the relation between the nerve 

 cord and the sperm duct (vas deferens) is constant : — the right 

 sperm duct always passing under the nerve cord in one species and 

 to the left in the other. In some cases where the external specific 

 differences are so small as to require the closest examination for 

 their detection the positional relation of the ducts of the repro- 

 ductive organs to the nerve cord will set aside the difficult}-." 



The histology of the male duct corresponds on the whole with 

 C. plana (Whitman, '91) and the different parts probably perform 

 the same functions; the enlarged portion of the duct (vs) serving 

 as a reservoir for mature spermatozoa, and the enlarged terminal 



