ON DINOPHILUS GIGAS. 113 



granular interstitial cells are replaced by elements secreting a 

 more or less sticky mucus. By means of this secretion the 

 animal can attach itself with some degree of firmness to foreign 

 objects. 



Closely attached to the ectoderm is the central nervous 

 system, which consists of a brain and a pair of lateral ventral 

 nerve-cords. 



The brain (fig. 3, n. /. + n. c.) entirely fills the prse-oral 

 lobe. It consists of a central mass of nerve-fibres {n. f.) sur- 

 rounded by ganglion cells (n. c). Embedded in its substance 

 are the two eyes (e), each consisting of one or two cells loaded 

 with granules of deep red pigment, surmounted by a small 

 cuticular lens. 



The lateral nerve-cords (figs. 4, 5, 6,8) are everywhere 

 in close contact with the skin. Large anteriorly, they grow 

 gradually smaller in passing backwards (cf. figs. 4 and 8) till 

 in the last segment they altogether disappear. Each cord con- 

 sists of a mass of fibres (fig. 4, n. /.), which is in the anterior 

 region more or less completely separated from the skin by 

 nerve-cells [n. c.) ; in passing backwards, however, the nerve- 

 cells almost entirely disappear, and it is to this that the dimi- 

 nution in size of the cord is chiefly due. 



No trace of commissures between the cords, nor of any 

 branches, could be found, though the presence of well-deve- 

 loped regions of sense hairs, already referred to, makes it cer- 

 tain that some kind of peripheral nervous plexus exists. 



Just above the nerve-cords, throughout the whole length of 

 the trunk, runs a small bundle of longitudinal muscle-fibres 

 [l. m.). These, and the ventral circular fibres already men- 

 tioned, are the only traces of a muscular system which could 

 be found. The walls of the alimentary canal, except a small 

 part of the pharynx, and apparently the whole dorsal region 

 of the body, are entirely destitute of muscles. 



The space between the body wall and the alimentary canal is 

 everywhere traversed by strands of connective tissue, which 

 forms a network with large spaces between the meshes. There 

 is no trace of an epithelial boundary to the spaces thus formed, 



VOL. XXV II, PART 1. NEW SEK. H 



