286 



CCELHELMINTHES 



Tylenchus tritici and Hcterodera schachti, the first doing great damage to wheat, 

 the second to turnips in Europe. T. devastatrix attacks rye and hyacinths. 



Family 2. ASCARID^E. Mouth with three lips; males with two spicules. Nu- 

 merous species in lower vertebrates, Ascaris lumbricoides,* the round worm of 

 man (fig. 246), inhabits the small intestine, often in enormous numbers. The 

 females are. about 5-6 inches, the males 4 inches in length. A female contains 

 about 60,000,000 eggs. Shortly after fertilization the eggs pass out with the 

 faeces, but develop without intermediate host if, in the course of two or three 



FIG. 246. Dorsal, end, and ventral views of head and hinder end of male Ascaris 



lumbricoides (from Hatschek.) 



months, when . the embryo is formed, they are taken into the human 

 intestine. The development of the pinworm, Oxyuris vermicular is*- is some- 

 what similar except that the embryos are developed in the egg at the time of 

 oviposition, and hence after a shorter stay outside the body are capable of in- 

 fection. The white worm, not half an inch long, lives in the rectum, especially 

 of children, and causes intolerable itching. Ascaris mystax* occurs in dogs 

 and cats (occasionally in man). A. megalocephala* (a favorite animal for 

 cytological researches) and Oxyuris equi in the horse, do little harm. Heterakis 

 maculosa often destroys whole flocks of pigeons. Family 3. STRONGYLUXE. 



o 



FIG. 247. Anterior end of hook worm, Ankvlostoniii duodenale (after Looss). 

 di, lower teeth; g, lateral gland; m, oral capsule; p, dorsal tooth; o, oesophagus; v, ven- 

 tral teeth. 



These are readily recognized by the bursa of the male, a broadening of the 

 hinder end of the body by two wing-like processes, which contains two spicula. 

 Frequent but not constant is a widened capsule surrounded by papillae at the 

 mouth. Strongyltts* in domestic animals. Syngamus frachealis,* half to three 

 quarters of an inch in length, the male and female always in pairs, cause the disease 

 known as 'gapes' in fowl. Ankylostomum (Dochmius) duodenale* (fig. 247), 

 about two fifths of an inch in length, lives in the small intestine of man, causing 

 severe loss of blood. The eggs develop in moist earth, and hence people who 



