180 P, HERBERT CARPENTER. 
no rows of pores at the sides of the ambulacra. But the 
hydrospires communicate with the exterior by ten inter- 
radial slits, which extend along the sides of the ambulacra 
very much as the bursal clefts do in the recent Ophiurids. 
The abradial walls of the burs also exhibit traces of the 
plicated structure which is so characteristic of the hydro- 
spires of the Blastoids. This comparison is one of great 
interest from many points of view, but a discussion of the 
questions it involves would be out of place here. 
Miiller’s views respecting the nervous system of the 
Ophiurids, although attacked by Lange, have been abun- 
dantly confirmed by Teuscher, Simroth, and Ludwig. All 
these four observers describe a band of tissue (fig. 4, 2) which 
lies immediately above the under arm plates (S;—S,, &c.), 
and is composed of two layers, an outer cellular and an inner 
fibrillar one. Lange considers this to be merely a portion 
of the integument, and has described as nervous a so-called 
ganglionated cord lying above it, very much as he did in 
the case of the Asterids. The other observers have shown 
the untenability of this view, the “ganglion cells”? being 
merely portions of the epithelial wall of the perihemal 
canal, while the “ longitudinal commissures”’ are portions 
of the membranous septum which separates the latter from 
the real nerve band. JHach radial nerve gives off two 
branches to the burse, which leave it just on the aboral side 
of the origin of the nerves proceeding to the second pair of 
buccal feet. The radial nerves are connected in the disc 
with an oral ring (27, 29), which is immediately contiguous 
to the blood-vascular ring and to the outer oral perihemal 
ring-canal (fig. 4, ”.7.). With the latter are connected five 
interradial spaces, one of which lies on the adoral side of the 
external interradial muscle of every oral angle, and is con- 
nected with the celom. Separated from the outer ring- 
canal by a septum! is the inner one (fig. 4, ¢.p.), from 
which arises the axial perihemal canal that encloses the 
central plexus and sand-canal, just as is the case with its 
fellow in the Asterids. The perihemal systems of the two 
groups are essentially similar, except that the Ophiurids 
lack the lacunar system which is so abundantly developed 
within the integument of the Asterids. 
1 It is evident from fig. 4 that the inner and outer perihemal ring-canals 
ot the Ophiurids are much more distinctly separated than they are in the 
Asterids. The former is separated from the body-cavity by the septum 
marked s, which must not be confounded with the perforated septum 
within the ring-canal of the Asterids; that supports the oral blood-vas- 
cular ring (figs, 5, 6, 8, s), ; 
