234 ZOOLOGY 
is produced into five radial and five short interradial caeca. 
The walls of the stomach are lined by a ciliated epithelium, 
Fic. 136.—Diagram of a transverse 
section of an Ophiuroid. 
1. Radial nerve, with lateral 
branches. 
bo 
So-called radial blood-vessel. 
Radial water-vascular trunk. 
Tube-foot. 
Ventral plate. 
oo 
oO 
Lateral plate. 
Ambulacral ossicles. 
Dorsal plate. 
Cs) CONT OD 
Dorsal portion of coelom. 
~_ 
<= 
Muscles. 
pao 
= 
. Lateral nerve. 
12. Origin of lateral nerve. 
and are supported by connective tissue strands, which traverse 
the coelom to the body-wall. There is no anus. 
The water-vascular system consists of a circumoral ring, 
which bears four Polian vesicles; in the fifth interradius it 
gives off the ciliated stone canal, which is simple and un- 
calcified, this passes to the madreporic plate on the ventral 
surface. In Astrophyton there are five madreporic plates, one 
in each interradius, and five stone canals. The radial vessels 
which arise from the ring bear no ampullae, but give off 
branches which pass directly to the conical tube-feet. Cor- 
puscles tinged with haemoglobin occur in the water-vascular 
fluid of one species. 
The true vascular system resembles that of Asterids. The 
aboral ring has, however, an undulatory curve, being ventral 
in the interradii. MacBride has recently proved that both the 
axial sinus and the aboral ring are involutions of the coelom. 
The so-called heart is nothing but a genital stolon, whence the 
genital rhachis grows out. The genital stolon in the earliest 
