NEMATODA ASCARIDAE 



141 



ova; the latter are fertilised by the sper- 

 matozoa, and give rise to rhabditiform 

 embryos, which escape by the alimentary 

 canal and form the free-living sexual 

 stage mentioned above. Thus in the 

 life-history of this form we find an alter- 

 nation of generation, a sexual free-living 

 form alternating with a hermaphrodite 

 parasitic form. 



Of the enormous number of other 

 species of the genus, only a very few can 

 be mentioned. A. transfuga Eud. in- 

 habits bears ; A. leptoptera Eud., lions ; 

 A. ferox H. and Ehrbg., Hyracoidea ; A, 

 depressa Eud., vultures ; A. rubicunda, 

 Schn., pythons ; A. sulcata Eud., turtles ; 

 A. mucronata Schn., the cod and pike ; 

 A. incurva Eud., the sword-fish. 



Oxyuris is Meromyarian (see p. 137), 

 and is characterised by the long capillary 

 tail of the female. It includes another 

 human parasite, 0. vermicularis, and it is 

 one which it is difficult to get rid of. 

 The female has the characteristic tail 

 and is about 10 mm. long. The male is 

 smaller. They are found in the caecum 

 and rectum of man, and cause great irri- 

 tation and sometimes serious functional 

 disturbance. The eggs are laid in immense 

 numbers but perish in water. If whilst 

 still in the egg-shell the larvae are 

 swallowed on fruit or raw vegetables, etc., 

 they are set free in the stomach and 

 small intestine by the action of the 

 digestive secretions. The distribution 

 of this parasite is universal. Besides 

 numerous species that inhabit the ali- 

 mentary canal of Vertebrates, such as 0. 

 ambigua Eud., found in hares and rabbits ; 0. curvula Eud., in 

 1 Arch. Zool. cxpcr. 1 ser. torn. vii. 1878, p. 283. 



FIG. 69. A male and female 

 Qxywris diesingi Ham. t'w 

 cojda. x 60. , Auus ; 

 b, oesophagus ; c, bulb ; d, 

 testis ; e, intestine ; /, 

 ovary. (From Caleb. 1 ) 



