774 PROFESSOR J. STEPHENSON 



of a new seta of the slender type. We can therefore actually see the change in the 

 character of the setse taking place. 



The body-ivall and muscular system call for only two remarks. The first is that 

 the cells of the lateral line are well seen in stained preparations as a very definite 

 band of nuclei ; the other, that a pair of muscular bands pass in each segment, one 

 on each side, from the dorsal to the ventral setal sac. Each band consists of a single 

 fibre which traverses the body-cavity in a vertical direction, and to which a nucleus 

 is attached ; in position they are comparable to similar bands in the Tubificidse (for 

 example, Branchiura, Limnodrilus, 5). 



The ccelomic corpuscles are spherical nucleated bodies, very variable in size, their 

 diameter being from 9 to 22 m- ; they contain a number of retractile, colourless 

 granules. In sections they are well seen ; and the cell-wall appears as a definite 

 membrane, from which the contents sometimes have shrunk away (text-fig. 5, a). 

 They originate mainly from the peritoneal lining of the dorsal body-wall. In the 

 anterior segments of the body behind the first few, masses of such cells are con- 



Text-fig. 5. 



spicuous, regularly segmental in their arrangement, in the free space dorsal to the 

 gut ; similar but smaller and less conspicuous aggregates may be seen also in the 

 posterior part of the body. These masses apparently represent the origin of the 

 ccelomic corpuscles ; the individual corpuscles of the mass can sometimes be seen to 

 be attached to the body-wall by protoplasmic bridges, by stalks, or by longer thread- 

 like strands (text-fig. 5, b). 



The chloragogen pigment has an unusual and characteristic distribution. In 

 most Naididee it extends forwards on the alimentary tube to about segment vi, or 

 perhaps v, and there ceases. In the present species it extends forwards as far as 

 the pharynx, the hinder part of which, in segment iv, it envelops (fig. 1, chl. 111 ) ; in 

 segment iii the pharynx is almost free from the pigment, which, however, again 

 extends round the anterior end of the pharynx, immediately behind the level of the 

 mouth, in the second segment (chl. 11 ). In the latter situation it forms a conspicuous 

 aggregate behind the cerebral ganglion ; and, further forwards still, a mass of brown 

 pigment is to be seen in the prostomium (chl. 1 ), anterior and ventral to the ganglion. 

 This distribution rendered the animals capable of immediate identification amongst 

 numerous others of different species. 



The chloragogen cells on the intestine and surrounding the dorsal vessel may 

 have in them very little of the pigment, which is much more densely aggregated in 



