234 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
strands traverse the rays (7s), while the latter gives origin 
to similar strands which are distributed to the genital 
elands (gs). There are also two strands which pass from 
the central plexus to the pyloric portion of the gut (ghs). 
On the aboral face of the disc, between the origins of two 
of the rays, is a rounded or pentagonal, more or less convex 
plate, the madreporite (Pl. XXXVIII, fig. 2, m). Tits 
surface 1s traversed by meandering grooves, radiating from 
the centre. Numerous perforations through its substance 
(Pl. XXXVI, figs. 1 and 2; Pl. XXXIX, fig. 1, mp) con- 
duct the surrounding water into a tubular canal, supported 
by ring-like ossicles lodged within its walls, the water- 
tube or stone-canal (Pl. XXXVIII, fig. 2; Pl. XXXIX, 
fig. 1, wt). 
Passing downwards towards the oral aspect, the water- 
tube opens into a pentagonal vessel which surrounds the 
mouth, the circum-oral water vessel. (Pl. XX XVIII, figs. 
land 2; Pl. XXXIX, fig. 1, cowv). In Astropecten and 
Lwdia five pairs of glandular ceca, the ‘‘ brown bodies” 
of Tiedemann (bb) are seated, interradially, upon the 
inner border of the circum-oral water vessel, and commu- 
nicate with its cavity. In Astertas and Solaster one of 
these bodies is absent from the madreporic interradius. 
The circum-oral water vessel has also. communicating 
with it a number of sacs with muscular walls, the Polian 
vesicles (Pl. XXX VIII, fig. 1, pv). These open upon its 
outer border, immediately opposite the brown bodies, and 
are, therefore, interradial. In Astropecten and Solaster 
the Polian vesicles are large and pear shaped, while those 
of Astertas are small and inconspicuous. From the 
circum-oral water vessel, vessels corresponding in number 
with that of the rays radiate (Pl. XX XVIII, figs. 1 and 2, 
rwv) and traversing the oral aspect of its ray, immediately 
external to the conjomed inner ends of the ambulacral ~ 
