218 



COMPARATIVE ANATOMY 



CHAP. 



In the Acanthocephala (Fig. 172, p. 258) there lies at the base of 

 the proboscis sheath a ganglion which sends several nerves forwards 



to the proboscis sheath, the pro- 

 boscis, and the neck. Posteriorly 

 there proceed from the ganglion 

 two lateral longitudinal nerves, 

 which first enter the retinacula 

 at the posterior end of the pro- 

 boscis sheath and run in them to 

 the body wall, and then to the 

 posterior end of the body. A 

 dorso- median longitudinal nerve 

 has also been observed. In the 

 male, besides the anterior gan- 

 glion, another ganglion in the region 

 of the genital apparatus (lying 

 anteriorly on the base of the 

 withdrawn bursa) has been de- 

 scribed; this gives off nerves to 

 the genital apparatus, and is also 

 connected by two nerves with the 

 posterior ends of the lateral longi- 

 tudinal nerves of the body. 



FIG. 142. Diagram- 

 matic representation of 

 the nervous system of 

 the Nematoda, after 

 Biitschli. on, Upper, un, 

 under portion of the oeso- 

 phageal ring; sg, lateral 

 swellings of the same; 

 vln, medio- ventral ; din, 

 medio-dorsal longitudinal 

 nerve ; c, commissures be- 

 tween the two ; hsn, pos- 

 terior lateral nerves (bur- 

 sal nerves). 



The nervous system of the Acantho- 

 cephala is up to the present time not 

 clearly understood. If there really is a 

 medio-dorsal longitudinal nerve it per- 

 haps corresponds with the medio-dorsal 

 nerve of the Nematoda, and then the 

 lateral longitudinal nerves perhaps repre- 

 sent the ventral longitudinal nerves, 

 which fuse in the middle line in most 

 Nematoda. What the relations are be- 

 tween the cesophageal ring of the Nema- 

 toda and the ganglion of the proboscis 

 sheath of the Acanthocephala, or whether 

 any such relations exist, are questions 

 which must be left on one side. 



FIG. 143. Cen- 

 tral nervous sys- 

 tem of Hirudo 



The Gordiidce also deviate from 

 other Nematoda in the structure 

 of the nervous system. Kound 

 the rudimentary pharynx lies a 

 medicinaiis, after ganglionic mass (peripharyngeal 

 Hermann. ganglion) which is much thickened, 



chiefly ventrally, and is produced into a ventral chord (Fig. 170, p. 

 256). This runs backward in the middle line and swells into a caudal 

 ganglion under the terminal portion of the genital ducts. In the male 



