268 J. H. ASHWORTH. 



Near its termination in the tail segment the cord gives off a 

 pair of comparatively large nerves supplying the anal cirri. 



In transverse section the nerve-cord is oval in shape, being 

 flattened from above downwards (fig. 17). In some speci- 

 mens it is very much flattened in the posterior region of the 

 animal; whereas in others it is not so compressed. 



Ganglion cells occur along the whole length of the cord, 

 being placed on the ventral face and at the ventro-lateral 

 angles. These cells are small and subequal, although here 

 and there a few larger cells may be seen generally situated 

 near the median line in the fissure between the two fibrous 

 tracts. The fibrous matter of the cord is partially sub- 

 divided into two by a median vertical sheet of neuroglial 

 tissue, the fibrillge of which form, in transverse section, a 

 network, more obvious in the ventral portion of the cord. 

 In horizontal sections the neuroglial fibrillai form wavy 

 strands resembling the neuro-fibrillge, but the former are 

 generally more deeply staining than the latter. 



In older specimens there is a proportionately greater 

 amount of fibrous matter in the cord, and the cells are 

 restricted almost entirely to the ventral face, and most of 

 them are situated in the small fissure between the fibrous 

 tracts, there being very few at the ventro-lateral angles of 

 the cord. In such specimens (30—56 mm, long) the neuri- 

 lemma sheath and neuroglial network are more highly de- 

 veloped than in younger specimens. 



The brain and nerve-cord, and especially the latter, are 

 poorly supplied with blood. 



There are two cords (fig. 16, Int. N.), best developed in 

 old specimens, running along almost the whole length of the 

 intestine. They are situated in the ventral wall just below 

 the ciliated groove. They are composed chiefly of fibrous 

 elements, but cells are present at frequent intervals. From 

 their appearance and structure they seem to be nervous, but 

 I have been unable to find any connection between them and 

 any other part- of the nervous system. The cords become 

 gradually smaller as they approach the posterior end, and 

 finally coalesce. They may be traced as far as the anus. 



