HIRUDINEA. 



523 



Generative organs. The Hirudinea are hermaphrodite. As in 

 many marine Planaria, the openings of the male and female organs 

 are placed one behind the other, the male being anterior, in the 

 middle ventral line of the anterior region of the body. In ^irudo 

 medicinalis the male opening, which in the Gnathobdellidae is pro- 

 vided with a protrusible penis, is in the segment 

 of the 6th distinct postoral ganglion (llth segment 

 counting the suboesophageal ganglion as consisting 

 of 6 fused ganglia), and the female opening in the 

 segment behind (Fig. 424). 



The reproductive glands are hollow structures, and 

 are continuous with their ducts. 



There are usually several pairs of testes arranged 

 segmentally, but in Nepkelis they are arranged irre- 

 gularly. In Hirudo (Fig. 424) there are nine or 

 ten pairs of testicular vesicles, which are connected 

 by short ducts with a sinuous vas deferens on either 

 side. Each vas deferens is coiled in front to form 

 a kind of epididymis (Fig. 425), and is then prolonged 

 into a muscular portion, the ductus ejaculatorius, 

 which unites with that of the other side to form 

 an unpaired eversible organ called the penis, with 

 the internal end of which is connected a well- 

 developed gland the prostate. The female apparatus 

 (Fig. 426) consists either of two long tubular ovaries 

 -extending over several segments (Clepsine, Nephelis), 

 or of two short saccular structures. The ovaries may 

 either join together at the genital opening (Clepsine), 

 or their walls may be continued as the two oviducts, 

 which soon join. The single oviduct so formed becomes convoluted, 

 and passes through the albumin gland, after which it becomes dilated 

 and constitutes the vagina which opens to the exterior (Fig. 426). 



The reproductive cells are produced by the cells lining the re- 

 productive glands, which must be regarded as special parts of the 

 coelom (sinus system) which have become shut off from the rest in 

 continuity with their ducts. This separation of the generative part 

 of the coelom from the rest takes place as we have seen in some 

 Oligochaeta. 



The spermatozoa are united together in packets the spermato- 

 phores. There does not appear to be any true copulation, but the 

 ;spermatophores are deposited on the body of another leech, whence 



FIG. 425. -Genera- 

 tive organs of the 

 Medicinal Leech. 

 T testis ; Vd vas 

 deferens; Nh 

 epididymis ; Pr 

 prostate; C 

 penis; Ov ovaries 

 with vagina and 

 female genital 

 opening. 



