ANIMAL PARASITISM 



451 



Numerous ectoparasitic trematodes, of the Subclass Monogenea, 

 occur on the skin and gills of fish and are often of economic im- 

 portance because they kill goldfish and other aquarium fishes, and 

 also young fishes in state fish hatcheries. 



Proboscis (extruded) 



Nerve-ganglion 



Egg 



7ol]c-cell8 



.< Intestine 



-Genn-celte 



Cercarl» 



Vectnl sucker. 

 Mephridium 



'Genn>eellf 



spoSfyst^-^Vfn^H^ ;iwLi^o^%-^"''^^^ Tiepaftca. A, egg; B, miracidium ; C, 

 l^SSt^fkn^^^.iJ'r^'^?'^< ^^^"^^^^^ '.y' ^"cy«ted stage- i/, adult (showing 



dWf^Qfivo orwi ^AC^r' '^"''^^' ^\' v.ci^d,ija,; tr, eiicystea stage; ±t, adult (showing 

 Company ^^^^^^tory systems). (From Hegner. College Zoology, The Macmillan 



