ECHINODE11MATA. 



native element, and watch the admirable spectacle which it then 

 presents : slowly he perceives its rays expand to their full stretch, 

 hundreds of feet are gradually protruded through the ambulacral 

 apertures, and each, apparently possessed of independent action, 

 fixes itself to the sides of the vessel as the animal begins its march. 

 The numerous suckers are soon all employed, fixing and detaching 

 themselves alternately, some remaining firmly adherent while others 

 change their position ; and thus, by an equable gliding movement, 

 the star-fish climbs the sides of the glass in which it is confined, 

 or the perpendicular surface of the submarine rock. 



But it is not only as agents in locomotion that the ambulacral 

 suckers are used ; helpless as these creatures appear to be, they 

 are among the most formidable tyrants of the deep, as will be 

 readily admitted by any one who watches them in the act of de- 

 vouring prey. When seizing its food, the rays of the Asterias 

 are bent towards the ventral aspect so as to form a kind of cup, 

 in the centre of which is the opening of the mouth ; the cup thus. 

 formed will, to a certain extent, lay hold of a passing victim, but, 

 without other means of securing it, the grasp would scarcely be 

 very formidable to animals possessed of any strength ; armed, how- 

 ever, as the rays have been found to be, with hundreds of tena- 

 cious suckers, escape is almost impossible, for prey once seized 

 is secured by every part of its surface, and, in spite of its utmost 

 efforts, is speedily dragged into the mouth and engulphed in the 

 capacious stomach, where its soft parts are soon dissolved. 



But to continue our survey of the class before us. Having ar- 

 rived at the point at which, by the diminution of the rays and 

 consequent extension of the central part, the body has assumed 

 a pentagonal outline, we may now advance in an equally gradual 

 manner to those globular species, of which the Echinus, or sea- 

 urchin, is the type or most perfect example. 



(183.) Echinidce. In the Scutellce (fig. 61), we have a flat and 

 shield-like body, in which even the angles of the margin are lost, 

 and the whole circumference acquires a circular form ; but still the 

 five radiating ambulacra are visible upon the centre of the disc, al- 

 though evidently imperfectly developed when compared with those 

 of the Asteridse above-mentioned. The nature of the integument 

 has, in fact, become so changed in its texture, that another modi- 

 fication of the locomotive organs is here imperatively called for, 

 and the means of progression are therefore proportionately altered. 

 In the Asteridse, the integuments, especially upon the dorsal as- 



