continue posteriorly into a lance-like point. The male is 3 to 5 

 mm., the female 10 mm. in length. The development is direct. 



Trichuris trichiura (Trichocephalus tridiiurus) lives parasitically 

 in the human intestine. The male is 40 to 45 mm. in length, the 

 female somewhat longer. The anterior part of the body is narrowed 

 into a thin whip-like structure, from the presence of which the 

 term whip-worm as applied to this species is derived. 



Strongyloides stercoralis is a minute nematode occurring in two 

 generations. A parasitic form in the human intestine, sometimes 

 regarded as a female reproducing parthenogenetically, is of about 

 2.2 mm. in length, the eggs of which develop in the lumen of the 

 intestine or mucosa of the host. A free-living form, differentiated 

 as males and females, the latter of about 1 mm. in length, develops 

 with higher temperatures outside the body, the females producing 

 about 40 eggs which develop into larvae. The latter give rise to 

 the parasitic phase. 



The parasites known as hookworms include two important 

 forms which occur commonly in the southern United States, by 

 reason of having a general distribution in the warmer zones and 

 doubtless introduced largely through the importation of negroes 

 from Africa. The forms are Ancylostoma duodenale and Necator 

 americanus. They are scarcely distinguishable externally but 

 differ in small details of structure. A. duodenale is about 9 mm. in 

 length in the male and 12 mm. in the female. There is an open 

 buccal capsule, the aperture of which is directed dorsally, the 

 interior containing small recurved hooks. The posterior end of the 

 body in the male is modified into an expanded bursa supported 

 by a number of rays. In the female the somewhat round end of the 

 body is supplied with a short sharp spike formed from the cuticle. 

 The organism lives in the human intestine, infection taking place 

 through water, contaminated food or through wounds on the skin. 



Many nematode parasites are adapted for living in the tissues. 

 The disease, primarily of the muscles, known as "Trichinosis", is 

 caused by a minute worm Trichinella {Trichina) spiralis. The 

 male is about 1.5 mm., the female 3 to 4 mm. in length. They begin 

 their parasitic phase in the intestine of the infected animal, the 

 latter being one of the lower mammals and commonly the pig, from 

 which the infection passes to man through insufficiently cooked 

 pork. The male remains in the intestine of the host but the female 

 burrows through the intestinal wall and produces live young to 

 a number of about 1,000. The embryos pass around through the 

 medium of the lymph spaces and ultimately find their way into the 

 muscles where they become encysted. They may remain in this 



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