220 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



described become gradually less obvious, and near the 

 anus practically disappear. 



Traversing the whole length of the mid-ventral line 

 of the animal is a shallow groove which marks the position 

 of the ventral nerve cord (fig. 6). Just behind the middle 

 of the third annulus (i.e., a short distance in front of the 

 first cheetigerous annulus) this groove unites with two 

 others which pass round the sides of the peristomium in 

 an antero-dorsal direction to the nuchal organ. These 

 are termed the metastomial grooves ; they indicate the 

 course of the oesophageal connectives. 



External Apertures. 



The mouth, when the proboscis is withdrawn, is a 

 crescentic transverse slit on the antero-ventral aspect of 

 the peristomium. It is overhung by a small upper lip, 

 and bordered all round by a series of papilla? (fig. 2). 



The anus is terminal, opening on the end of the last 

 tail segment. Through it the terminal part of the intes- 

 tine occasionally protrudes for a short distance. 



The nuchal organ is a transverse crescentic, or V- 

 shaped, ciliated sensory groove formed by invagination of 

 the epidermis of the sides and hinder end of the pros- 

 tomium (fig. 5). The prostomium may be withdrawn 

 into this groove so as to be almost hidden from view. 



The openings of the otocysts are minute and difficult 

 to see. They may, however, be found in large specimens. 

 They are situated dorso-laterally in the peristomium close 

 to the point where the metastomial groove crosses the first 

 inter-annular groove (fig. 5). 



The openings of the six pairs of nephridia are small 

 oval slits situated immediately dorsal and slightly 

 posterior to the upper ends of the fourth to the ninth 

 neuropodia (figs. 1 and 19). 



