ANATOMY OF THE NEMATODES 267 



or six ; behind the anus it divides and combines with the lateral 

 nerves. The latter consist of two fasciculi at either side extend- 

 ing to the hindermost part one dorsal and one ventral which in 

 the greatest part of the body do not run in, but next to, the 

 lateral ridges, and exhibit a different origin in the front. The 

 ventral fasciculus at each side branches off from the ventral 

 median nerve in front of the excretory pore, whereas the dorsal 

 fasciculi originate from the pharyngeal ring close to the lateral 

 ganglia. Each of the four fasciculi contains only two or three 

 fibres, which run backwards parallel to the lateral ridges ; a few 

 centimetres in front of the caudal extremity they join the lateral 

 ridges 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 arch-like manner. 



In the male each ventral part of the lateral nerves becomes 

 thickened by taking up fibres from the ventral nerves, which become 

 thickened posteriorly to the nervus bursalis, which towards the 

 middle gives off a mass of fibres to the " genital papillae " situated 

 in front of and behind the anus ; the number of these fibres 

 averages 80 100 ; in its further course the bursal nerve resembles 

 the corresponding ventral part of the lateral nerves of the female. 



The ventral and dorsal nerves " are connected by a number of 

 semi-circular commissures, which originate from the ventral nerves 

 and serve to supply the dorsal nerve, which is always being 

 decreased by fibres departing from it. It is remarkable that these 

 commissures are not placed symmetrically, and their position also 

 is different in the two sexes ; in the female there are thirty-one 

 on the right side and only thirteen on the left side. In the male 

 there are thirty-three commissures on the right side and fourteen 

 on the left, which run into the sub-cuticular layer generally in 

 pairs, and usually cross at the level of the lateral ridges. 



The fibres of the two median nerves are chiefly motory ; 

 fascicular processes run from each protoplasmatic part of the 

 muscular cells to the median nerves ; from these they take up 

 bundles of primitive fibrils, which separate, pass through the proto- 

 plasmatic part and enter the contractile part (fig. 182). One part 

 of the fibrils, however, penetrates . beyond the muscles into the 

 subcuticular layer, where they form a network, probably of a 

 sensory nature, with contiguous fibrils. Nerves directed anteriorly 



