398 



ANNELIDA. 



line of the anterior region of the body. The male generative 

 opening lies in front of the female and is usually provided with a 

 protrusible cirrus. The testes lie in pairs in several successive 

 segments and are usually present in considerable numbers (fig. 322). 

 In Hirudo there are nine or ten pairs of testicular vesicles, which 

 are connected with a sinuous vas deferens on either side. Each 

 vas deferens is coiled in front to form a kind of epididyniis (fig. 

 322, NK) and is then prolonged into a muscular portion, the ductus 

 ejaculatorius, which unites with that of the other side to form an 

 unpaired copulatory apparatus. This is in connection with a well- 

 developed prostatic gland (Pr), and can be protruded either as a 

 two-horned sac (Rhyncobdellidce) or as a long filament (Gnathob- 

 dellidce). The female generative apparatus consists either of two 

 long tubular ovaries with a common opening to the exterior 



(RhyiwcibdelMdcB), or of two short 

 saccular ovaries, two oviducts, a 

 common duct surrounded by an al- 

 bumin gland, and a dilated vagina 

 with the genital opening (Gnathob- 

 dellidcK) (fig. 323). In copulation 

 a spermatopkore passes out of the 

 male genital organs, and is either 

 received into the vagina of the 

 other animal or at least becomes 

 attached within the generative 

 opening. In any case the fertili- 

 zation of the ovum takes place with- 

 in the body of the mother. The egg 

 is laid soon after. For this purpose 

 the animals seek suitable places on stones or plants, or leave the water 

 and, as Hirudo medicinalis, burrow in damp earth. At this period 

 the genital rings are swollen out into the form of a saddle, partly by 

 the turgescence of the generative organs and partly by the great 

 development of the cutaneous glands, the secretion of which is of 

 special importance to the fate of the eggs which are about to be 

 laid. When the eggs are about to be laid, the leech attaches itself 

 firmly by its ventral sucker and, twisting itself about, envelops the 

 anterior part of its body with a viscid mass, which covers especially 

 the genital rings like a girdle and gradually hardens to form a 

 firmer membrane. A number of small eggs and a considerable 

 quantity of albuminous matter then pass out, and the animal with- 



FIG. 323. a, Cocoon, b, female genera- 

 tive apparatus of Ulritdo medicinalis 

 (after R. Lcuckart). 



