NEMATODA. 



351 



to be the lateral surfaces of the moving animal. Most Nematoda 

 are parasitic, but lead an independent life in certain stages of their 

 life history. Numerous small Nematoda, however, are never parasitic, 

 but live freely in fresh and salt water and in the earth. Some 

 Nematodes are parasitic in plants, for example, Anguillula tritici, 

 dipsaci, etc. ; some live in decaying vegetable matter, e.g., the 

 vinegar worm in fermenting vinegar and paste. Nevertheless very 

 similar forms occur in the contents of the intestine and in the faeces 

 of different animals and of man (A. intestinalis, stercoralis). The 

 power possessed by small Nematoda of resisting the effects of pro- 

 longed desiccation and of coming to life again on being moistened 

 is very remarkable. 



Fam. Ascaridse. Body tolerably stout. With three lips furnished with 

 papillee. One of these lips is. directed towards the dorsal surface, while the two 

 others meet together in the ventral 'line. The posterior end of the male is 

 ventrally curved, and usually furnished with two horny spicula. 



FIG. 283. Axcarii lumbricoides (after R. Leuckart). a, Posterior end of a male with the two 

 spicula (Sp). b, Anterior end from the dorsal side, with the dorsal lip furnished with 

 two papillae, c, The same from the ventral side with the two lateral ventral lips and the 

 excretory pore (P). d, Egg with the external membrane formed of small clear spherules. 



Ascaris L. Polymyarian, with three strongly developed lips, the edges of 

 which are in the larger species provided with teeth. The pharynx is not sepa- 

 rated as a distinct bulb. The caudal extremity is usually short and conical, 

 and in the male sex invariably provided with two spicula (fig. 283, a). A. 

 luwibricoidcs Cloquet, the human round worm, a smaller variety in the pig 

 (J.. suilla Duj.) The eggs pass into water or damp earth and remain there 

 some months, until the embryonic development is completed ; they are probably 

 carried into the alimentary canal of their later host by means of an inter- 

 mediate host. A. megalocephala Cloquet (horse and ox) ; A. mystax Zed. 

 (cat and dog), sometimes parasitic in man. 



Oxyuris Eud. Meromyarian ; usually with three lips, which bear small 

 papillge. The posterior end of the oesophagus is enlarged to a spherical bulb 

 provided with a masticatory apparatus. The posterior end of the body of the 

 female is thin and pointed, while that of the male has only two prseanal and few 

 postanal papillae, and a single spiculum (fig. 279). O vcrmicularis L., in the 

 large intestine of man, distributed in all countries. The female is about ten 

 mm. long. 0. curvula Eud., in the caecum of the Horse. 



