Page:Popular Science Monthly Volume 13.djvu/341

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specimens give us but little idea of this animal. It must be seen and studied while in the sea or in the aquarium, in order to be appreciated. When dead, the suckers—which are like those of starfishes and sea-urchins—are retracted, and the tentacles are also in a mass, and the

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Fig. 28.—Cake-Urchin (Echinarachnius parma, Gray). Fig. 29.—Key-Hole-Urchin (Mellita quinquetora, Agassiz).

whole form is shriveled. But in the water the form is full, and the fringed tentacles are extremely beautiful, and can properly be compared to the delicately-branched and beautifully-colored sea-weeds which we all so much admire.

The "sea-cucumber" has a wonderful power of changing its form. It elongates, contracts, enlarges at each end while it is small in the middle, and thus changes its appearance from time to time. In its power of going to pieces it almost excels the "brittle-star" and the

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Fig. 30.—Holothurian, or "Sea-Cucumber" (Pentacta frondosa), North Atlantic.

starfish, Luidia, already noticed. It breaks off its tentacles, and yields up other parts, at will; and it has been known, when disturbed, to eject all its internal organs, thus leaving itself only an empty sac!

The "sea-cucumber" has no hard parts, excepting the merest calcareous particles imbedded in the thick, leather-like covering. These