330 ECHINODERMATA. 
ORDER I. 
PEDICELLATA. 
The Pedicellata are distinguished by organs of motion ex- 
clusively peculiar to them. ‘Their skin is pierced with a 
number of little holes, arranged in very regular series, through 
which pass cylindrical and membranous tentacula, each one 
terminated by a little disk which acts like a cupping-glass. 
_ That portion of these tentacula which remains within the 
body is vesicular ; a humour is effused through their entire 
cavity, and is either propelled at the will of the animal into 
the exterior and cylindrical portion, which it distends, or re- 
turns to the interior vesicle, when the former sinks and be- 
comes relaxed. It is by thus elongating and shortening their 
hundreds of little feet or tentacula and by fixing them by 
their cup-like extremities, that these animals effect their pro- 
gressive motions. Vessels proceeding from these feet extend 
to trunks which correspond to their ranges, and which ter- 
minate near the mouth. They form a system distinct from 
that of the intestinal vessels observed in some species(1). 
Linneus divided them into three very natural, but nume- 
rous genera, and composed of such various species, that they 
may be considered as forming three families. The 
ASTERIAS, Lin. 
Or Starfish, have been so called because their body is divided into 
rays (generally five), in the centre of which, and underneath, is the 
mouth, that is also the anus. 
(1) For details respecting the organization of the Star-fish, Ursini and Holo- 
thurie, see the splendid anatomical Monograph of Tiedemann, Landshut, 1816, 
in folio. 
