128 NEMATHELMINTHES CHAF. 



nerve splits it swells out into an anal ganglion situated just 

 in front of the anus. In the male l this anal ganglion gives oft' 

 two lateral nerves which pass round the cloaca and form a 

 ring, and in this sex the ventro-lateral nerve, which is much 

 strengthened by fibres from the ventral nerve, and has received, 

 owing to the mistaken impression that it was a special ncrvus 

 recurrens, the name of the " bursal nerve," gives off numerous 

 branches to the sense papillae which are found in this region of 

 the body and on the tail. The arrangement of these parts is 

 shown in Fig. 63. 



Sense organs are but poorly developed in the Nematoda, as is 

 usual in animals which are, as a rule, either parasitic or live 

 underground. Eyes, consisting of masses of dark pigment with 

 or without a lens, occur in the neighbourhood of the circum- 

 oesophageal nerve -ring in some free-living forms. Leuckart has 

 described some hollow vesicles with granular contents lying near 

 the left excretory duct, just where it bends in towards the pore, 

 which may possibly be of the nature of auditory organs ; but the 

 chief sense organs are the papillae, of which in A. megalocephala 

 there are two kinds, the lip papillae being distinguished from the 

 genital papillae by the fact that the nerve supplying them ends 

 in a fine point and pierces the cuticle in the former case, whilst 

 in the latter it swells out into an " end-organ," which is always 

 covered by a layer of cuticle, though sometimes by a very thin 

 one. 



Muscular System. The muscular system is one of the most 

 characteristic features of the Nematoda, both as regards the 

 histology of the muscle-cells and the way in which the cells are 

 arranged. 



Each muscle-cell is of considerable size, and is of the shape of 

 a somewhat flattened spindle produced into a process near the 

 middle. Each end of the spindle cell is said to be continuous 

 with the fibrils of the sub-cuticular layer. 2 The muscle-cell 

 consists of two portions, a contractile part which lies next the 

 sub-cuticle, and which usually, to some extent, wraps round the 

 second or medullary half. The latter consists of a fibrillar 

 spongioplasm, in the meshes of which lies a clear structureless 

 hyaloplasm. The nucleus always lies in the medullary half. 



1 E. Rohde, Zool. Beilr. Bd. i. 1885, p. 11. 

 E. Rohdc, ZovL Anz. xvii. 1894, p. 38. 



