Page:Popular Science Monthly Volume 13.djvu/328

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 * PSM V13 D328 Cnidae or lasso cells.jpg
 * 1. Lasso-cells of an Actinia, with the lasso coiled within—its actual length $1/350$ of an inch. 2. The same as 1, with the lasso extended. 3 and 4 are alike—the former with the lasso coiled within, and the latter with the lasso extended. 6, 7, 8, 9, 10, a lasso-cell in different stages of development.
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 * 1. Lasso-cells of an Actinia, with the lasso coiled within—its actual length ⇭⇭⇭ of an inch. 2. The same as 1, with the lasso extended. 3 and 4 are alike—the former with the lasso coiled within, and the latter with the lasso extended. 6, 7, 8, 9, 10, a lasso-cell in different stages of development.
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On various parts of the sea-anemones, and of all other polyps, especially on their tentacles or fringes, there are very remarkable objects called cnidæ, or lasso-cells, like those on jellyfishes, each cell being less than one two-hundredths of an inch in length. In each there is a long, slender, coiled, and wonderfully-constructed thread, which can be instantly darted forth, paralyzing any little animal which it strikes; and thus the hungry polyp secures its food.

On the vertical partitions above mentioned the eggs are borne. These pass out into the water through the mouth. The newly-hatched anemone is oval in form, and swims freely about in the water by means of exceedingly delicate fringes called vibratile cilia. After a time it quits this roving life, attaches itself to the surface of the rocks, and grows into the form and size of the parent.

Sea-anemones have no proper nervous system. The sense of touch is distributed throughout the whole animal. It will, therefore, appear as a remarkable statement that some kinds have quite definitely-formed eyes. These are seen in some tropical species just outside of the tentacles, and according to Dana each of these eyes has a crystalline lens and an optic nerve!

Sea-anemones readily reproduce lost parts. If one is quickly torn from a rock, parts of the foot remain attached to the rock, and in many cases each portion thus left will become a perfect sea-anemone!

Sea-anemones vary greatly in size. Some species are only a