146 BULLETIN: MUSEUM OF COMPARATIVE ZOÖLOGY. 
layer, gradually diminishing in diameter, till it terminates, just 
beneath the external epithelium of the peristome, The corre- 
spondingly tapering lumen, posteriorly continuous with the body- 
savity, ends blindly within the apex of the cone. The base of 
the cone (Plate 4, fig. 45) is incomplete on its abaxial side, 
connective-tissue fibers there crowding up into its lumen, which 
is thus partially filled. 
This nerve protuberance consists of exactly the same kind of 
elements as the nerve ring. Nerve fibrillae run through it longi- 
tudinally; nuclei, comparable with those of the covering epithelium, 
are distributed over its outer surface, and from them arise the 
ordinary supporting fibers, which run radially toward the central 
lumen of the cone, against the wall of which they terminate. 
The lumen, which in the specimen examined contains numerous 
blood corpuscles, is continued behind the junction of cone and nerve 
ring by a wall composed of (1) an inner layer continuous with the 
peritoneal epithelium, (2) longitudinal muscle fibers, and (3) the 
connective tissue of the integument. 
In the specimen in which this conical nerve protuberance was 
found the tentacles and other parts of the aquapharyngeal bulb 
were in all respects normal. 
b. Nerves arising from the Radial Bands. 
Although I have found it difficult to determine the exact dis- 
tribution of all the nerve fibers which lie in bundles on either side 
of the radial nerve, it can be distinctly seen that the inner nerve 
band distributes fibers to the transverse (Plate 4, fio. 43) and longi- 
tudinal museles of the body-wall, whereas the outer band inneryates 
chiefly the integument, Both the inner and outer bands, more- 
over, furnish a rich supply of nerve fibers to the walls of the rudi- 
mentary lateral ambulacra. (Plate 6, fig. 79). 
As regards the distribution of its fibers, the inner nerve band 
in Caudina resembles the corresponding layer in ophiurans and 
echinoids, for in both of these groups, as Cuénot (91) has shown, it 
distributes its branches to muscles, It should be noted, however, 
that in the Cucumariidae and ITolothuriidae Hérouard has found 
that the internal layer innervates to a large extent the integument, 
and Cuénot also finds that it takes part with the external layer 
