ANATOMY. PHYSIOLOGY, ETC. 
Ech. 9 
subdivided by a (sometimes incomplete) longitudinal vertical septum, 
and by more or less complete horizontal longitudinal septa ; the inner- 
most (proximal) of these chambers unite to form an external vascular 
ring, close to which lies another, internal, which gives off two delicate 
vessels, running along each arm in the longitudinal septa. From both 
sides of these central-neural vessels (not demonstrated, however, in 
Asterias pr.), short lateral vessels spring, encircling the feet, and united 
by four other longitudinal vessels, thus forming a regular angular 
meshwork along each ambulacrum ; the most external of these longitu- 
dinal vessels on each side communicate with the outer vascular oral 
ring. How the chambers of the neural vessels are filled by injection 
from the ring, is still a mystery. The heart appears to be an abortive 
functionless organ in the adult ; in the young, it is a dense convolute of 
delicate vessels : it is enclosed within the “ sack-shaped organ,” which 
springs from the internal neuro- vascular ring, and afterwards embraces 
the stone-canal, accompanying it to the madreporite,” which puts the 
two vascular systems in communication with each other and with 
the sea- water. From the “ sack-shaped organ ” the anal ring was easily 
injected in Echinaster, and shown to consist of 2-3 parallel vessels ; 
it gives off the ovarian vessels, but the vencn intestinales of Tiedemann 
are apparently abortive, if vessels at all. The ampullae of the suckers 
have, in Astropecten and Luidia, a vigorous muscular coating, which is 
wanting in those Asteridcu of which the suckers are provided with discs. 
Lange (10), on the other hand, describes the ampullae of Asterias ruhens 
as highly muscular ; and though he describes the septa dividing the space 
between the nervous band and the ambulacral water-tube very much in 
the same manner as Teuscher, his conception of the histological com- 
position of the band and of the limitation of its nervous and dermal 
elements is much at variance with that of Teuscher. Its tissue is only a 
qualitative modification of the common epithelium of the starfish. The 
cones which form the ocelli of the composite eye of the starfish, are 
formed of pigment cells, bearing on their heads clear rod-like bodies, 
converging towards the axis of the cone. The cavity of the terminal 
feeler is the continuation of the ambulacral aquatic vessel. Lange also 
describes a valve on each side of the orifice, between the suckers and the 
ambulacral vessel, forming an obstacle for the reflux of the liquid during 
the contraction of the feet or ampullas. 
Anatomy of Ophiuridm. In the cavity between the ventral arm-plates 
and the inferior surface of the “ ambulacral vertebrae” lies, according to 
Teuscher, innermost (uppermost) the ambulacral aquiferous vessel ; it 
gives off, in pairs, branches for the feet, and communicates with the 
more external of the two annular vessels, which are located in the meta- 
morphosed vertebrae, forming the central body-skeleton round the mouth. 
In some species, Polian vesicles are attached to this outer, or ambulacral, 
vascular ring ; one of these vesicles, communicating with the “ madre- 
porite ’’-mouth-shield, is the “ stone-canal.” Below the ambulacral water- 
tubes of the arms, the neural blood-vessel is situated ; it encloses the 
nerve-trunks on both sides, and gives off, for each “ vertebra,’’ a ring- 
vessel, which reposes in its peripheral furrow, and is subdivided at its 
