1 66 



NEMATHELMINTHES 



ch; 



serve various functions ; between tliese splits strands of tissue are 

 left which form mesenteries, and some of the cells remain lining 

 the muscular layer (Fig. 86). These cells have been described 

 by Vejdovsky as a definite somatic, peritoneal epithelium, but 

 this was not found by von Linstow. Besides forming the mesen- 

 teries, and acting as packing between the various organs of the 

 body, these cells also form the ova and the spermatozoa. 



The splits which have appeared when the animal has reached 

 the second larval stage, are two dorsal and a ventral; the latter 

 contains the alimentary canal, and may be termed the body-cavity, 

 the former will develop the generative organs. The mouth is 

 occluded in the older larvae, and in the adults there is a dis- 

 tinct but solid oesophagus which passes into a tubular intestine. 

 The intestine consists of a single layer of cells surrounding a 

 lumen ; it runs straight to the hinder end of the body, where it 

 opens in both sexes with the ducts of the reproductive organs. 

 The nervous system consists of a well-defined circumoesophageal 



ring with two dorsal 

 swellings, and, arising 

 from this, a median ven- 

 tral cord which runs the 

 whole length of the 

 body. The cord consists 

 of three longitudinal 

 strands with ganglionic 

 cells below them ; the 

 latter, though they lie 

 within the muscle layer, 

 maintain a connexion 

 with the hypodermis. 

 Behind, the nerve-cord 



Fig. 84. Section through a young female Gordius ,. ,, , 



tolosanus. (From von Linstow.) a, Cuticle ; 6, Splits in the male, One 



hypodermis ; c, muscular layer ; d, parenchyma ; half passing into each 

 e, alimentary canal ; /, nervous system ; g, egg- t 



sac ; h, ovary. caudal fork. In the 



adult a pair of black 

 eyes can be detected on the head; the only other sense organs 

 are the tactile bristles mentioned above. Excretory organs are 

 unknown. 



The generative organs only attain maturity in the adult, which 

 is, in fact, exclusively devoted to reproduction. No trace of testes 



