126 NEMATHELMINTHES CHAP. 



enclosed muscle - cells into four quadrants. These thickenings 

 surround dorsally and ventrally a specialised nerve-cord, and 

 laterally the excretory canals. 



According to Jammes 1 this lack of differentiation in the sub- 

 cuticular layer is caused by the early appearance of the cuticle, 

 which he thinks is necessitated, at any rate in many of the 

 parasitic forms, by the action which the digestive juices of the 

 host would have on the otherwise unprotected body-wall. 



FIQ. 62. A transverse section through the body of Ascaris transfuga Rud., in the region 

 of the oesophagus : a, the muscular oesophagus with its triradiate lumen ; b, the 

 cuticle ; c, the sub-cuticle ; d, the muscular layer ; e, the lateral nerves running in 

 the lateral line ; /, the excretory canal ; g, the dorsal, aud h, the ventral nerve ; i, 

 the triradiate rod iu the fin. 



The nervous system, according to the same writer, is of the same 

 nature as this sub-cuticular tissue, only it is more differentiated, 

 or perhaps we should say it has retained more of the primitive 

 cellular character of the embryonic tissue. The fibres of the 

 sub-cuticular tissue are closely connected with the fibrils which 

 compose the spongioplasrn (Fig. 64, rf) of the muscles, 2 and form 

 also the sheaths of the various nerves ; in fact the passage of 

 these fibrils into the nerves is so gradual that it is impossible 

 to make any separation between them. 



1 Ann. Sd. not. 7, ser. vol. xiii. 1892, p. 321. 



2 E, Rohde, SB. Ak. Berlin, 1S92, p. 515. 



