. Harper's young people . Fig. 1.—UNDER SURFACE OF A SEA-URCHIN, SHOWINGKows OF SUCKERS AMONG THE SPINES. Through theseholes are pro-truded the dou-ble rows oftube-feet, justlike those wehave studiedin the star-fishand worked inthe same man-ner. It addsmuch to thebeauty and in-terest of theshell to knowthat these love-ly fine dotsare openingsthrough which the tube - feet are supplied with water from inside the shell. In the dia-gram (Fig. 4) the madreporic body is shown at /, and thetube-feet with their little water-bags at p. Sea-urchinsmove by means of their tube-feet, which may be lengthen-
. Harper's young people . Fig. 1.—UNDER SURFACE OF A SEA-URCHIN, SHOWINGKows OF SUCKERS AMONG THE SPINES. Through theseholes are pro-truded the dou-ble rows oftube-feet, justlike those wehave studiedin the star-fishand worked inthe same man-ner. It addsmuch to thebeauty and in-terest of theshell to knowthat these love-ly fine dotsare openingsthrough which the tube - feet are supplied with water from inside the shell. In the dia-gram (Fig. 4) the madreporic body is shown at /, and thetube-feet with their little water-bags at p. Sea-urchinsmove by means of their tube-feet, which may be lengthen-ed so as to extend far beyond the spines. The shell fits the animal exactly in its infancy, and muststill serve it in old age, for urchins never cast off theircoats as crabsor lobsters form-ed of manysmall pieces,it grows a lit-tle all over, as. Fig. 2.—SHELL OF SEA-URCHIN WITHOUT SPINES. show you. Eachplate is sur-rounded byliving flesh se-cretes limefrom the seawater and de-posits it roundthe edge of the plates, thus increasing the size of the shell sea-urchins die the spines drop off; the shell is sofrail that it too is soon broken, the plates falling apart. Do not omit to look at the spines with your micro-scopes, and see what beautifully carved columns theyare (Fig. 3). Falling about on the back of the urchin,they remind one of a sadly neglected grave-yard with its tottering spine is hollowed atthe end to fit a knob on theshell. This forms a per-fect ball-and-socket joint,which is supplied with del-icate muscles to move thespines. As the creaturetravels along the spines areconstantly working, andthey look as if they toowanted to help. In somespecies the spines are verylarge, and they are used forslate-pencils. We shouldthink it quite luxurious tohave such artistic pencils,but m
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Keywords: ., bookcentury1800, bookdecade1870, bookpublishernewyo, bookyear1879
