222 



UNSEGMENTED WORMS 



Most are ectoparasitic. The development is direct and associated with 

 one host (monogenetic). 



e.g. Polystonium integerrimum, with many posterior suckers, often 



in the bladder of the frog. It attaches itself in its youth to 



the gills of tadpoles, passes thence through the food canal 



to the bladder. 



Gyrodactylus, on the gills and fins of fresh-water fishes. It is 



Fig. 1 20. — Male and 

 female Bilharzia — 

 Schistosomum hcemato- 

 bium. — After Looss. 



The male is about three- 

 fifths of an inch long ; the 

 female (F.), carried in the 

 ventral groove or gynaeco- 

 phoric canal {G.C.), is four- 

 fifths. S., Anterior suctorial 

 mouth ; P.S., the adhesive 

 sucker. On the surface of 

 the male's body there are 

 numerous minute papillae. 



viviparous, but the embryo, before it is extruded, itself 

 contains an embryo, and this in turn another. 



Diplozoon paradoxum consists of two individuals united. 

 The single larva (Diporpa) is at first free-swimming, 

 but becomes a parasite on the gills of a minnow, 

 and there two individuals unite very closely and per 

 manently. 



Tristomum, with three suckers, on some marine fishes. 



