TREMATODA. 



225 



end of the body (Amphistomum). The large sucker may however 

 be absent (Monostomum). The ectoparasitic forms are, on the other 

 hand, distinguished by a much more powerful adhesive armature ; 

 for, besides two small suckers at the sides of the mouth, they possess 

 one or more large suckers at the posterior end of the body \ Fig. 185), 

 which, moreover, may be supported by a chitinous framework. 

 There are often in addition chitinous 

 hooks, and very frequently two 

 larger hooks among the posterior 

 suckers in the middle line (Fig. 

 185). In the . Temnoceplialidae the 

 anterior suckers are replaced by a 

 group of tentacles, and in the Aspi- 

 docotylea the adhesive apparatus is 

 a kind of large ventral foot bearing 

 numerous suckers. 



Reproductive organs. The 

 Trematoda are mostly hermaphro- 

 dite. * As a rule, the male generative 

 opening and the uterine opening of 

 the female are side by side or one 

 behind the other, not far from the 

 middle line of the ventral surface, 

 near the anterior end of the body 

 (Fig. 179). The openings may be 

 separate, or they may lead into a 

 genital cloaca which opens by the 

 single genital pore. The male open- 

 ing leads into sac, the cirrus sac, 

 which encloses the protrusible ter- 

 minal part (penis or cirrus) of the 

 vas deferens. The vas deferens soon 

 divides into two, which lead back 

 to the two large simple or multi- 

 lobed in Distoinum liepaticuin 



much branched testes. Both testes and ovaries are, as a rule, 

 placed between the two limbs of the intestine. 



The female organs consist of a convoluted uterus and of an ovary 

 and paired yolk-glands, to which may be added a special shell-gland. 



* Bilharzia, Distomum Okenii, and perhaps one or two other Digenca are 

 dioecious. 



Do 



FIG. 179. Distoinum hepaticum (after 

 Sommer). mouth ; D caecum of in- 

 testine (hinder part of intestine not 

 shown) ; S sucker ; T testes ; Do yolk- 

 glands ; Dr ovary ; Ov uterus. 



