//. NEMATHELMINTIIES : NEMATODA. 



299 



The mouth connects with the miiscuhir (esophagus, which, for 

 sucking purposes, is expanded posteriori}' to a pliaryngeal bulb and 

 is lined throughout with a cuticle. From this point to the anus 

 the stomach-intestine is usually uniform (fig. 363). The oi-sopliagus 

 is surrounded by a nervous ring which sends forward and back a 



V-_-_ 



Fig. 203. Fig. 264. 



Fig. 263.— Structure of young female Ascaris (based on a drawing by Leuekart). 

 rf, intestine: ", ovary; .s, lateral line: x\ ventral line: va, va).^ina. 



Fig. 264.— Diaeram of nervous system of a nematode. (After Butschli.) c, commis- 

 sures; d, dorsal nerve: (, infracjesophageal, .s, supraoesophageal part of nerve 

 ring : r, ventral nerve. 



large number of nerves, those in the mid-dorsal and ventral lines 

 being strongest. At points on these nerves are collections of 

 ganglion cells, but a formation of ganglia, as in the annelids, does 

 not occur (fig. 264). 



The sexual organs of these rarely hermaphroditic forms are 

 very simple. Males and females are easily distinguished not only 

 by the copulatory organs, but by the openings of the genital ducts. 

 These, in the male (fig. 205), are in the end of the alimentary 

 canal, which hence is a cloaca. In the female (fig. 203) there is a 

 special genital opening on tlie ventral surface between mouth and 

 anus, the position varying with the species. In general the struc- 



