146 



THE EFFECTS OF PARASITES ON THEIR HOSTS. 



Two Trematodes^ — 



Distomum hepaticum (F). 

 „ lanceolatum (G). 



Four JSTematodes — 



Ascaris lumbricoides (A). 

 Oxyuris vermicularis {B, C). 

 Trichocephalus dispar {D). 

 Dochmius duodenalis {E). 



They all produce eggs of such characteristic form and size (see 

 figure), that one can, almost by a mere superficial inspection, refer 

 them to their parent animal. The eggs of the two species of Tcenia 



Fig. 90. — Eggs of worms found in the alimentary canal of man. ( x 400. ) 

 A, Ascaris lumiricoides; £,C, Oxyuris vermicularis ; D, Trichocephalus dispar ; 

 E, Dochmius duodenalis; F, Distomum hepaticum; 6, Distomum lanceolatum; S, 

 Tcenia solium ; I, Tcenia saginata ; K, Bothriocephalus latus. 



are the most difficult to distinguish. They differ almost solely in 

 that those of T. solium are somewhat more spherical, and on the 

 whole smaller, than those of T. saginata. The eggs of Distomum 

 hepaticum are the largest, and indeed gigantic, attaining a size of 

 0'135 mm. long by 0'083 mm. broad. They are nearly twice as long 

 as the eggs of Bothriocephalus latus and Ascaris lumbricoides, and 



^ These both live in the gall- ducts, out of which the eggs are only accidentally trans- 

 ferred to the alimentary canal. 



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