ECHINID^E. 167 



of these animals, the common Star-fish of our coast, which, as it lies 

 upon the sand, left by the retiring waves, appears so incapable of move- 

 ment, so utterly helpless and inanimate ; let him place it in a large 

 glass jar filled with its native element, and watch the admirable spec- 

 tacle which it then presents. Slowly its tapering 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 de- 

 taching themselves alternately, some remaining firmly adherent, while 

 others change their position ; and thus, by an equable gliding move- 

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

 or scales the perpendicular surface of the submarine rock. 



It is not only as agents in locomotion that the ambulacral suckers are 

 used ; for, 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 devouring prey. When seizing its 

 food, the rays of the Asterlas 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, 

 however, as the rays have been found to be, with hundreds of tenacious 

 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 engulfed in the capacious stomach, where 

 its soft parts are soon dissolved. 



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

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

 extension of the central part, the body has assumed a pentagonal out- 

 line, 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. 



(440.) ECHINID^E. In the Scutellce (fig. 84), 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 disk, although 

 evidently imperfectly developed when compared with those of the Aste- 

 ridae above-mentioned. The nature of the integument has, in fact, be- 

 come so changed, that another modification of the locomotive organs is 

 now imperatively called for ; and the means of progression are therefore 

 proportionately altered. In the Asteridse, the integuments, especially 

 upon the dorsal aspect, are always more or less composed of a coriaceous 

 material, or, at least, of solid pieces so articulated together as to permit 

 of considerable flexibility : but in the Echinidae the nature of the ex- 



