128 



NEMATHELMINTHES 



CHAP. 



nerve splits it swells out into an anal ganglion situated just 

 in front of the anus. In the male 1 this anal ganglion gives of 

 two lateral nerves which pass round the cloaca and form 

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

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

 owing to the mistaken impression that it was a special nervi 

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

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

 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 pf masses of dark pigment witl 

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

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

 described as possible auditory organs certain giant -cells lying 

 near the orifice of the excretory ducts. Later research has shown 

 these cells to have some phagocytic action on the contents of the 

 body -cavity. 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. Beitr. Bd. i. 1885, p. 11. 



2 E. Rohde, Zool. Anz. xvii. 1894, p. 38. 



