198 DISPERSAL OF PARASITIC EGGS 



I. Those not requiring an intermediate host. 



(a) Those in which the larval worm remains within the 

 egg-shell. 



Ascaris luinbricoides. 

 Toxascaris liinbata. 

 Belascaris my s tax. 

 Oxyin'is verui iailaris. 

 TricJuiris tricJiiurus. 

 Hymenolepis nana. 



{U) Those in which the larva is liberated from the egg- 

 shell and spends its life in water. 



Ankylostoma duodenale. 

 Necator americanns. 

 Schistosoninni hcBmatobium. 

 ScJiistosoninni japonicum. 



II. Those requiring an intermediate host. 



{a^ Those encysting in animals which are commonly 

 eaten by man. 



Trichinella spiralis in the pig. 

 Tccnia solium in the pig. 

 Tcujiia saginata in the ox. 

 Dibothrioceplialus latus in fresh-water fishes. 



ib) Those encysting in animals which may be swallowed 

 accidentally by man. 



Fasciola hepatica in pond snails and eventualh' on grass. 

 Dicroavliuni lanceatnni in slugs and pond snails. 

 Hynienolepis diininnta in fleas and other insects. 

 Dipylidiwn caninuni in fleas. 



" There are several other common human parasites of which 

 the life-history is entirely unknown. Of those in the above list, 

 the mode of infection of Schistosoninni lueniatobinni has not been 

 definitely proved, but it is probably similar to that of Schisto- 

 soninni japonicnni, the free-swimming larva of which is capable 

 of infecting directly. Tj'ichinclla spiralis is peculiar in being 



