138 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
1. CENTRAL NERVOUS SYSTEM. 
The central nervous system in Caudina resembles that of all 
other holothurians in being composed of a circular band, surround- 
ing the buccal opening, and of five equi-distant radial bands, each 
of which consists of an outer band, arising from the circular band 
and running backward in the radii to the tip of the tail, and of 
an inner band having the same general course. 
a. Circular Nerve Band. 
The nerve ring in Caudina does not lie within the calcareous ring, 
as is said to be the case in the Synaptidae, but anterior to it. Hence 
I have described this nerve band as surrounding the mouth rather 
than the pharynx. It is situated beneath a loose connective-tissue 
layer, immediately internal to the base of the tentacles (Plate 4, 
fig, 44). An epineural space (en. crc.) separates it from the con- 
nective tissue in front of it. In cross section the nerve ring is some- 
what elliptical (Plate 3, fig. 42, Plate 4, fig. 44); it is flattened in 
an anterior-posterior direction and to such an extent that the greater 
diameter may be 4—5 times the lesser one (242 w x 56 p), or it may 
be only 2—3 times as great (240 » x 93 »). A deep, narrow furrow 
runs round the nerve on the axial side of the anterior face, extend- 
ing obliquely outward and backward. It is of nearly uniform 
depth in any one specimen, measuring 56 » deep in sections of one 
individual, 72 » in those of another. The part of the nerve ring 
which forms the lining of the furrow presents the same cellular 
conditions as the rest of the anterior part of the circular band. 
The nerve ring, as in other holothurians, consists of delicate longi- 
tudinal fibrillae, which are interspersed with oval, lightly-staining 
nuclei of ganglionic cells. Its anterior surface is covered with some- 
what smaller, deeply-staming nuclei. From these nuclei, which 
belong to the Deckepithel of Hamann, arise coarse transverse fibers, 
more than twice the diameter of the nervous fibrillae (Plate 3, 
fig. 41). The cells which I have designated as ganglionic and 
which lie embedded within the nerve band consist each of a large 
oval nucleus, measuring on the average 4.25 » x 6.33 p, and a small 
amount of cytoplasm. From them probably arise the fibrillae which 
make up the principal part of the nerve band. These cells, which 
