224 Records of the Indian Museum. [Vora Vinlx 
mouth; on the other side there were no setae; the prostomium 
was very round, and the impression given wasthat the animal had 
not been long separated. A fifth specimen had no prebranchial 
setae on either side; the prostomium was very well marked,. the 
mouth and the structures of the head in general were well formed ; 
moreover this was the specimen in which asexual division was going 
on at the posterior end (pl. xi, fig. 4); it seems justifiable to suppose 
that this animal had been leading an independent existence for some 
time. A sixth specimen had similarly no prebranchial setae on either 
side ; the setae of the first gilled segment were smaller and thinner 
than those of succeeding segments; the differentiation of the head 
end of the animal was however incomplete, the shape, and the rela- 
tions of mouth and pharynx did not appear normal, and the gills 
ceased, even as tubercles, after the twenty-first segment; it seems 
not improbable, therefore, that this animal had only recently 
been separated, and had still to undergo a certain amount of 
development at this anterior end. The seventh specimen had no 
prebranchial setae, and setae were also absent on the first gill- 
bearing segment (pl. xi, fig. 3); the prostomium, mouth, pharynx 
and cerebral ganglion were well formed, and the animal had 
probably therefore been separated for a considerable time. 
It is perhaps worthy of remark that in the fifth and seventh 
of the above specimens the prebranchial region seemed to present 
a somewhat indefinite, thicker or denser appearance of the tissues 
and a consequent slight opacity, as compared with the segments 
behind it. Whether this is of any importance or not is perhaps 
doubtful ; but it reminded me of a similar somewhat denser and 
more Opaque appearance of the tissues which is seen at the hinder 
end, in any of the Naididae, in the region where new segments are 
forming but not yet differentiated. 
It is evident, in any case, that the distribution of setae 
in the anterior part of the body varies very considerably. So far as 
I am aware, such marked variations have not been neticed in any 
other form. Further remarks on the import of this variability 
will be found below. 
Other anatomical features.—In sections through the middle of 
the body, the sides of the animal are seen, in these specimens, to 
be somewhat pinched in; and at the level of each septum a distinct 
band of muscular fibres passes on each side from the lateral line 
to the gut; it is presumably the contraction of these fibres that 
causes the constriction referred to. 
The pigment cells, asseen in sections, are large irregular cells, 
containing a large number of brown granules, and indeed appearing 
to be made up of them (pl. xi, figs. 5,6). The cells occur in several 
situations,—(a) round the dorsal vessel and lateral commissures, 
(b) along the muscular fibres passing through the coelom from gut 
to parietes, (c) inside the muscular layer of the body-wall, (d) 
apparently more or less free, as corpuscles inside the body-cavity, 
attached however to the inner surface of the parietes by processes 
of the pigment cells themselves, or of other corpuscles. 
