34 MR. W. K. HUTTON ON THE [Jan. 20, 
From the brain two pairs of nerves arise. ‘The first pair 
(Plate VIII. fig. 16, B), which are very slender, take their origin 
from the ventral aspect of the ganglionic mass just anterior to the 
eye-spots; from them twigs pass to supply the epineural canal and 
apparently also the two dorsal tentacles. The remaining tentacles 
receive their nerves from the two stout cir cumesophageal con- 
nectives (fig. 16, A), which constitute the second pair of nerves, 
and arise ventro-laterally behind the eye-spots, coursing round 
the base of the tentacular crown, between it and the muscular 
tube formed by the fusion of the retractor muscles. Ventrally, 
the circumecesophageal commissures unite to form the nerve-cord. 
This shoavs no trace of segmentation. Dorsally it is composed of 
fibres, while ventrally nerve-cells are distributed evenly along its 
whole length. It is accompanied laterally by two fine muscles, as 
is usual in the Sipunculide. 
Sense-Organs. 
In tracing back series of sections, there becomes apparent on 
the dorsal wall of the pharynx a patch of long-celled columnar pig- 
mented epithelium. The cells of this layer are found (Plate VIII. 
figs. 12, 13, 14, 15, 8.E.) to be the dorsal wall of a slit-like canal, 
whose ventral wall is formed by cells which, on the one hand, cover 
the brain in front, and on the other are continuous with the non- 
ciliated epithelium which clothes the outer aspect of the two 
dorsal tentacles (8.V.), which are seen in fig. 12 to have united 
along their mesial margins. 
Posteriorly the canal thus formed (which may be called the 
epineural canal) becomes very narrow centrally, and ends blindly 
by dividing into two little cals-de-sac (8.P., fig. 15), which 
project downwards and outwards into the cerebral cortex, and are 
lined by a columnar epithelium the cells of which are deeply laden 
with granules of a reddish-black pigment. 
The cup-like organs thus formed are usually called ‘“ eye-spots,” 
and are present in at least four other species of Phascolosoma, but, 
so far as ] am aware, no account of their structure has hitherto 
been published. Their existence In an animal which lives at a 
depth so great as that of 60 fathoms is noteworthy, and appears 
to me to argue for the organs in question some function other than 
even merely photometric ; but asmall fraction of diffused daylight 
can permeate so far. ‘They are always to be found in the genus 
Phymosoma, and from the above-given description it will be seen 
that the sense-organs of Ph. teres resemble in the main those of 
Phymosoma varians (Shipley, 7). They differ, however, from 
those of Phymosomea in their relations to the tentacles. 
In the genus Phymosomea the cells entering into the formation 
of the eye-spots are continuous, on the one hand, with theepithelium 
covering the anterior aspect of the brain, and, on the other, with 
those which constitute the lming of the mesial surface of the 
tentacles. In Phascolosoma, on the contrary, the sensory epi- 
