140 
described become gradually less obvious, and near the 
anus practically disappear. 
Traversing the whole length of the mid-ventral lne 
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 (?.¢., 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 
ave termed the metastomial grooves; they indicate the 
course of the esophageal 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The mouth, when the proboscis is withdrawn, is a 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 papill (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 The prostomium may be withdrawn 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), 
