GEROULD: CAUDINA. 139 
are here much more numerous than in the radial bands, are fre- 
quently arranged in long lines parallel to the direction of the circular 
band, their nuclei being so oriented that their long axes extend in 
the same direction. 
The nuclei of the covering epithelium (Hamann’s Deckepithel) 
differ from those of the ganglionic cells in their smaller size 
(4 x 5.33 ») and in the fact that they stain more deeply. The 
fibers proceeding from them, which, with Hamann, I regard as 
non-nervous supporting structures, run through the substance of the 
nerve ring perpendicularly to the direction of the band and in an 
antero-posterior direction. The deep ends of these fibers are often 
swollen, as Hérouard has described them in Cucumaria ; their conical 
tips abut against the underlying connective tissue. I have found that 
in Caudina the nuclei of the covering epithelium are evenly distrib- 
uted, not being especially numerous in the interradii. Jourdan (83), 
on the contrary, found them in the forms which he examined heaped 
together in the interradial parts of the nerve ring. 
b. Radial Nerve Bands. 
Each radial nerve consists in Caudina (Fig. 40, 43) of (1) a thick 
outer band, —crescentic in cross section,— which arises from the 
nerve ring and terminates near the posterior extremity of a radius 
immediately below the epithelium, in front of an anal papilla, and (2) 
a thin inner band, which is closely apposed to the outer band — being 
separated from it by only a thin connective-tissue partition — and 
presents along the greater part of its inner surface a median furrow. 
The inner band divides anteriorly into two branches, each of which 
subdivides, to innervate the anterior ends of the radial longitudinal 
and the interradial transverse muscles of the body-wall, and disap- 
pears entirely as a band immediately posterior to the junction of 
the outer band with the nerve ring. Posteriorly the inner band 
accompanies the outer band to near the end of the radius. It ter- 
minates a little in front of the posterior extremity of the outer band 
with a slight enlargement (Plate 4, fig. 50). It sends nerve fibers 
to the circular musculature of the region and to a pair of rudimen- 
tary ambulacra lying opposite this point. Perhaps the ambulacra in 
question are also supplied by nerves from the outer band. 
Immediately external to the radial nerve is the radial epineural 
canal (en. 7.), which is continuous with the circular epineural canal, 
