ECHINODERMATA ASTEROIDEA The casual observer who should, for the first time, examine a star-fish, or a sea-urchin, two of the most familiar examples of the Echinodermata met with upon our shores, would indeed find it a difficult task to associate them with any other class, or to imagine the affinities whereby they are related, either to the simpler animals we have already described, or to more perfect forms of existence hereafter to be mentioned. They would seem to stand alone in the creation, without appearing to form any portion of that series of development which we have hitherto been able to trace. But this apparent want of conformity to the general laws of development vanishes on more attentive examina tion ; so that we may not only trace the steps by which every family of this extensive class merges insensibly into another, but perceive that, at the two opposite points of the circle, the Echi dermata are intimately in relation with the Polyps on one hand, while on the other they as obviously approximate the annulose animals, to which the most perfectly organized amongst them bear a striking resemblance. In Ophiurus, the rays are long and simple, resembling the tails of so many serpents—a circum stance from whence the name of the family is derived. Never theless, on each side of every ray we still trace movable lat eral spines, which, although but mere rudiments of what may be seen in Comatula, may still assist in locomotion, or perhaps may contribute to retain the prey more firmly when seized by the arms. The rays themselves are composed of many pieces curiously imbricated and joined together by ligaments, so that they are, from their length and tenuity, extremely flexible in all directions, and serve not only for legs adapted to crawl upon the ground, but are occasionally serviceable as fins, able to support the animal in the water for a short distance by a kind of undu latory movement. The body, or central disc, is beautifully con structed, being made up of innumerable pieces accurately fitted together. The mouth occupies the centre of the ventral surface, and is surrounded by radiating furrows, in which are seen minute apertures that give passage to a set of remarkable prehensile organs; these are calculated to act as suckers, and so disposed as either to fix the body of the animal, or to retain food during the process of deglutition. In Ophiurus we have just mentioned the existence of protrusible suckers around the opening of the mouth, well adapted, from their position, to take firm hold of food seized by the animal ; and it is by increasing the number of such organs that ample compensation is made for the loss of mo tion in the rays themselves in the star-fishes. On examining the
lower surface of an Asterias, even in those forms which most ap proximate a right-lined pentagon in their marginal contour, the number of rays will still be found to be distinctly indicated by as many furrows radiating from the mouth, and indicating the centre of each division of the body. These ambulacral furrows, as they are termed, exhibit, when examined in a dried specimen, innu merable orifices arranged in parallel rows, through each of which, when alive, the animal could protrude a prehensile sucker, capa ble of being securely attached to any smooth surface. No verbal description can at all do justice to this wonderful mechanism, even leaving out of the question the means by which each indi vidual sucker is wielded ; but let any of our readers, when oppor tunity offers, pick up from the beach any 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 movement, so utterly helpless and inanimate ; let him place it in a large glass . jar filled with its native element, and the admirable spec tacle 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 devouring 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 pos sessed of any strength ; armed, however, as the rays have been found to be, with hundreds of tenaceous 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.