136 



MANUAL OF ZOOLOGY 



integument. The leaf-like form exemplified in the Liver- 

 fluke prevails in most (Fig. 66), but a more elongated form 

 sometimes occurs. The anterior end is distinguished from 

 the posterior by its shape, by the arrangement of the suckers, 

 and, in many of those Trematodes that are external 

 parasites, by the presence of eyes. Suckers are universal in 

 their occurrence. They are always ventrally placed, their 



B 



FIG. 66. Trematodes. A, A niphistomum ; B, Homalogaster. g.p. genital 

 aperture ; m. mouth ; s. posterior sucker ; te. testes ; vit. vitelline glands. 

 (After M. Braun.) 



chief function being to fix the parasite to the surface of its 

 host in such a way as to facilitate the taking in by the 

 mouth of animal juices and epithelial debris. Their number 

 and arrangement vary considerably. There are nearly 

 always present an anterior set (or, as in the Liver-fluke, a 

 single anterior sucker surrounding the mouth), and a 

 posterior set or a single large posterior sucker. There are 



