505 
from the body of the cell, not being a continuation of a short process, 
as described above (Fig. 4, No. 3). 
The isolated sense cells are in greatest abundance over the 
prostomium, and anterior part of the body. Over the middle of the 
body they are less numerous. At the posterior extremity they are 
again abundant, though not to the extent found in the head region. 
It thus appears that these cells are most numerous on the ends 
of the body, the parts unprotected by the tube and in most intimate 
relation with the animals environment. 
So far as observed the sense cells bearing more than a single 
hair are confined to the prostomium, and about the first ten body 
segments. Miss F. E. LAnGDoN in a paper upon the{‘Nervous System 
of Nerias Virens”, shortly to be published in the “Journal of Com- 
parative Neurology”, describes a case seemingly parallel to this. She 
finds upon the anterior cirri of the worm, epidermal sense cells bearing 
several hairs; and attributes this condition to a restriction of the 
space available for sense cells, together with some condition, perhaps 
a necessity for extreme sensitiveness, which makes it necessary that 
the hairs be very close set over a considerable area. Over the anterior 
extremity of Tubifex, as it is thrust about through the mud, a 
restricted area is also called upon to do a large amount of work as 
a sensory apparatus and the same explanation of the presence of 
multihaired cells is suggested. 
B. Two to four sense cells frequently form a loose group. The bodies 
of the cells of such a group may be in contact, or may be separated 
by intervening supporting cells; but their necks are always separate, 
each projecting into a separate concavity in the lower surface of the 
cuticle (Fig. 4, Nos. 1 and 2 and Fig. 5, Nos. 1 and 2). The cells forming 
these groups are not visibly altered by their contact with, or proximity 
to, one another. The size of the cell, the location of the nucleus, the 
point of origin of the nerve fibre, and the size and relation of the 
tactile hairs, are the same as in isolated sense cells of the same 
region. There is no common cuticular elevation over the cells making 
up one of these groups; and the tactile hairs in their passage thro 
the cuticle are not gathered into one small bundle. These last two 
points serve to distinguish the groups of sense cells from the sense 
organs described below. 
These groups are present over all regions of the body; except 
the anterior extremity, where the great number of isolated sense cells 
render the groups indistinguishable, if present. The groups are numerous 
in the tube protected regions, where as many as four or five stained 
