GENERATIVE ORGANS OF VERMES. 



187 



V(T 



arrangement which obtains in the marine Planarians. There is 

 always a larger number of germ -glands (5-12 pairs : t) for the male 

 organ (Fig. 91) ; they correspond to a number of metameres, are 

 rounded bodies, and are arranged serially on either 

 side. A duct leads from each to a laterally-placed 

 vas deferens (vd), which widens internally, and be- 

 comes much coiled in front of the first pair of 

 testes (vs). From this coiled portion a terminal 

 piece, accompanied by its fellow of the opposite 

 side, passes to the genital pore. A large number 

 of glandular tubes (g) join the united efferent ducts, 

 and not unfrequently form, as in the Planarias, a 

 large mass of acini (Clepsine). Either the two 

 terminal tracts of the vas deferens function as copu- 

 latory organs, and, together with a portion of the 

 gland which surrounds them, project from the body 

 in the form of a vesicle (Clepsine, Piscicola) ; or 

 there is a special copulatory organ, which receives 

 the ends of the seminal vesicle. In this case (San- 

 guisuga, Hamiopis, etc.) the portion formed by the 

 union of the two seminal ducts is developed into 

 a strong muscular organ (i^), the thinner end of 

 which forms a short penis. As in the Planarias 

 and Trematoda, this lies in a penial pouch, which 

 opens at the genital pore, and from which it can 

 be protruded during copulation. 



The female organs, also, of the Hirudinea re- 

 semble in many points the organs of several Pla- 

 tyhelminthes (marine Planarias). The ovaries, which 

 in the latter are scattered through the body, are 

 here formed by two rounded, tubular, or lobate organs (o), which 

 lie near the middle line of the body, just behind the male efferent 

 organs. In some they open, merely by a short oviduct, at the 

 female genital pore (Leeches with a proboscis). In others the 

 efferent ducts are separated. The narrow oviducts give rise to a 

 longer common tract (Hirudo). The common duct, the several coils 

 of which are held together by a glandular layer, then widens into 

 a vagina at the terminal portion of the efferent duct (u). 



Fig. 91. Genera- 

 tive organs of a 

 Leech, t Testes. 

 vd Vas deferens 

 commune, vs Coiled 

 portion of the semi- 

 nal duct, analogous 

 to a seminal vesicle. 

 p Penis, g Glands. 

 o Ovaries, u Va- 

 giua. 



§ 154. 



In the Scoleina the organs lie in the anterior metameres, generally 

 occupying the tract between the eighth and fifteenth. Two different 

 types of the sexual apparatus are to be distinguished. One is well 

 marked in the Terricolre, and is characterised by the independence 

 of the efferent organs. The male part of the system in the Lum- 

 bricidas is formed by two pairs of testes, which are connected with 

 wide sacs, in which the elements of the semen are further developed. 



