ANATOMY OF THE NEMATODES 



365 



Pr. 



the lateral nerves on either side. In the male the median nerve 

 enlarges to nearly the original number of fibres in front of the anal 

 ganglion, which contains seven 

 cells ; there is also an anal ring 

 embracing the terminal gut, and 

 there are two ganglion cells in it on 

 each side. In the dorsal median 

 line the dorsal median nerve is alike 

 in both sexes ; arising in front with 

 a single root from the cesophageal 

 ring, it gathers its fibres from the 

 lateral ganglia ; in the anterior part 

 of the body it consists of thirteen 

 to twenty fibres ; in the posterior 

 part -of the body the fibres are re- 

 duced to four or six ; behind the 

 anus it divides and combines with 

 the lateral nerves ; the latter 

 consists of two fascicles at either 

 side right up to their most pos- 

 terior extent one dorsal and one 

 ventral which in the greater part 

 of the body do not run in, but 

 beside the lateral lines, and exhibit 

 a different origin anteriorly. The 

 ventral fascicle at each side branches 

 off from the ventral median nerve 

 in front of the excretory pore, 

 whereas the dorsal fascicles origin- 

 ate from the cesophageal ring close 

 to the lateral ganglia. Each of the 

 four fascicles contains only two or 

 three fibres, which run backwards 

 parallel to the lateral lines; a few 

 centimetres in front of the caudal 

 extremity they enter the lateral 

 lines and remain separate from one 

 another up to the level of the anal 

 ganglion ; here they amalgamate on 

 either side, after each interpolating 

 one ganglion cell, with the single 

 short lateral nerve which first takes 



up the forked ends of the ventral and then of the dorsal median nerve ; 

 finally, both lateral nerves unite with each other at the back in an 

 arch-like manner. 



FIG. 263. Schematic representation of 

 the nervous system of a male Ascaris mega- 

 locephala. A., anus; Ag. t anal ganglion; 

 C. t commissures ; D.m.n., dorsal median 

 nerve ; Exp., excretory pore ; Pr., oesopha- 

 geal sensory ring; Lg. , lateral ganglia; 

 Ln., lateral nerve; Sp., papilla; V.m.n., 

 ventral median nerve. (After Brandes. ) 



