

ZOOLOGY FOR MEDICAL STUDENTS 



CHAP. V 



ristence completely parasitic, passing from one individual 

 In T simply by bodily transference in the encysted condition. 



II. In Ascaris, Trichocephalus, Oxyiiris, the eggs pass to the exterior 

 .(1 fur a time a free existence but they complete their development 



i taken in by a second individual host. 



III. In Aucylostoma not merely the egg stage, but the young worms 



For a time free-living, but a return to the host is necessary 

 lor them to complete their development. In Dracunculus a similar 

 condition is found, with the additional complication however that the 

 : uikes its way into a second or intermediate host, of a species 

 ;t from the principal host : while in Filaria bancrofti, F. loa, and 

 /'. pcrstaus, the whole of the part of the life-history free from the prin- 

 cipal host i> passed within the body of. the secondary host. 



IV. In Asniris uigrovenosa, a common parasite in the lung of the 

 ordin.ii the young which pass to the exterior become sexually 

 mature and one or more generations of free-living individuals occur 



the return to the host. A somewhat similar life-history occurs 

 in the human parasite Strongyloides stercoralis. 



\ . In Angiiillula and its allies small nematodes which occur com- 

 monly in soil, in flour-paste, in vinegar (exhibited sometimes by showmen 

 under the mi< -roscope as " eels " in paste or vinegar) the parasitic phase 

 come completely eliminated from the life-history. 



HOOKS FOR FURTHER STUDY 



Brumpt. Precis de Parasitologie. 



Manson. Tropical Diseases. 



Castellani and Chalmers. Manual of Tropical Medicine. 



