. Evenings at the microscope : or, Researches among the minuter organs and forms of animal life . Zoology; Microscopy; Microscopes. SEA-URCHINS AND SEA-CUCUMBERS. 805 and unite, first into "T-, and then into H -forms, and then into irregular networks. Meanwhile, fleshy cylindrical columns spring up from the surface, one in each of these interspaces, and presently develop within their substance a similar framework of porous glass ; these soon manifest them- selves to be the spines, and each is seated on a little nucleus of network, on which it possesses the power of rotating. At the same t
. Evenings at the microscope : or, Researches among the minuter organs and forms of animal life . Zoology; Microscopy; Microscopes. SEA-URCHINS AND SEA-CUCUMBERS. 805 and unite, first into "T-, and then into H -forms, and then into irregular networks. Meanwhile, fleshy cylindrical columns spring up from the surface, one in each of these interspaces, and presently develop within their substance a similar framework of porous glass ; these soon manifest them- selves to be the spines, and each is seated on a little nucleus of network, on which it possesses the power of rotating. At the same time pedicellarise begin to be formed; and, what is specially marvellous, they are first seen, not on the disk, which alone is to be the future Urchin, but on the interior wall of the helmet, which is even now in pro- cess of being dissipated, and even on the opposite side to that which carries the disk. They commonly appear four in number, arranged in two pairs; and one can see in them —they being, like the suckers, large out of all proportion to the disk—the stem, and the three-leaved heads, which already exercise their characteristic snapping movements. The disk is meanwhile enlarging its area; and the spines and suckers, gradually lengthening, at length push themselves through the walls of the helmet; the hanging points and crest of which are fast diminishing by a kind of insensible absorption; the ci- liary movements become • less vigorous, and the mouth closes up. But, correspondently, the Urchin is beginning to acquire its own independent power of locomotion; for the suckers, now ever sprawling about, are capable of adhering to any foreign body with which they come into contact, and of drag- ging the whole structure about, by their proper contractions. The cilia that cover the thickened fringing band still exercise their powers, and are the last to YOUNG SEA-URCHIN : DEVELOPMENT OF Please note that these images are extracted from scanned page imag
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