. Evenings at the microscope : or, Researches among the minuter organs and forms of animal life . Zoology; Microscopy; Microscopes. 292 EVENINGS AT THE MICROSCOPE. since the contact of the edges with the stone is so perfect that no air can find entrance between them. Now the pressure of the atmosphere upon the leather is so great that a con- siderable weight, perhaps half-a- dozen pounds, may be lifted by the string before the union yields. Well, the very counterpart of this amusing operation is repeated by the clever "Urchin" whose performances we are considering. 6TJCKEE-PLAIK of t
. Evenings at the microscope : or, Researches among the minuter organs and forms of animal life . Zoology; Microscopy; Microscopes. 292 EVENINGS AT THE MICROSCOPE. since the contact of the edges with the stone is so perfect that no air can find entrance between them. Now the pressure of the atmosphere upon the leather is so great that a con- siderable weight, perhaps half-a- dozen pounds, may be lifted by the string before the union yields. Well, the very counterpart of this amusing operation is repeated by the clever "Urchin" whose performances we are considering. 6TJCKEE-PLAIK of techin. The tube is his string ; the dilated end with the plate in it his leather; his muscular power acts like the other urchin's tread, to press the bottom of the sucker against the surface of the rock. Then he pulls the string; in other words, he drags inwards the centre of the muscular bottom of the sucker, which is, as it were, sucked up into the central orifice of the plate. Thus a vacuum is formed beneath the middle of the sucker, on which the weight of the incumbent water and atmosphere united presses with a force far more than sufficient to resist the weight of bis body, when he drags upon it, and, as it were, warps himself up to the adhering point. Here is in my cabinet a specimen of a Sea-Urchin of a less regular form : it is the Heart-Urchin (Amphidotus cordatus). Essentially, its structure agrees with that of the more globular forms, but it is heart-shaped, and the two orifices, instead of being at opposite poles, are sepa- rated only by about one-third of the circumference. It shows also singular impressed marks on its shell, as if made by a seal on a plastic substance. But what I chiefly wish to direct your attention to are the spines. These differ much from the kindred organs in Echinus, being far more numerous, very slender, curved, thickening towards the tip, and lying down upon the shell in the maimer of hair, whence the species is sometimes. Please note that
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