182 ZOOLOGY. 
it is conveyed to each water-sac or ampulla (Fig. 125, am). 
These pear-shaped water-sacs, when contracted, are supposed 
to press the water into the long slender suckers or ambulacral 
feet, which are distended, elongated, and by a sucker-like ar- 
rangement at the end of the prehensile foot act in conjunc- 
tion with the others to warp or pull the star-fish along. 
Besides locomotion the ambulacral feet serve for respiration 
and perception (Simroth). Hoffman shows that the feet 
of the sea-urchins can be projected or thrust out without 
the aid of the ampulle. 
It will thus be seen that the water-vascular system in the 
star-fish is in its functions partly respiratory and partly 
locomotive, while it is in connection with the vascular sys- 
tem, and thus partly aids in circulating the blood and 
chyle. 
Of the true vascular or blood system the student can ordi- 
narily only discover one portion, the so-called ‘‘ heart ’’ or 
“* pulsating vessel,’’? which we may call the hemal canal (Fig. 
125, %),and which runs parallel to the stone-canal from the 
madreporic body to near the ring-canal.* It is nearly as 
large as the stone-canal, slightly sinuous, muscular, and with 
the latter is surrounded by a loose investing membrane like 
a pericardium. Some observers deny the existence of a vas- 
cular (sometimes called ‘‘ pseudohzmal ’’) system, but it has 
been recently studied by Hoffman and subsequently by. Teu- 
scher, who maintains that in all Echinoderms there are two 
systems of blood-vessels, which belong, one to the viscera and 
the other to the nervous system, forming an oral or nervous 
ring and an analring. The two rings are in direct com- 
munication in the star-fishes, Ophiurans and sea-urchins, 
but not in the Holothurians. The radial nerves are ac- 
companied by a vessel which subdivides and distributes 
branches to the ambulacral feet in star-fishes, Echini, and 
Holothurians. Teuscher considers that the “‘ heart ’’ found 
in the star-fishes and Kchini connecting the cesophageal (or 
nerve-ring) and anal ring, is neither a gland nor a pulsating 
vessel, as different authors have supposed, but perhaps only 
* Simroth states that in Ophiurans (Ophiactis) the stone-canal opens 
ia common with the ‘‘ heart’”’ into the madreporic plate. 
