Page:Popular Science Monthly Volume 24.djvu/504

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488
THE POPULAR SCIENCE MONTHLY.

ferent butterflies resting with their wings folded together on flowers, leaves, bark, old walls, dead wood, etc., and to the thousands of instances daily in which insects pass unobserved by being confounded in their general harmony with the objects that are nearest to them.

The shells which serve as houses to land-snails, and which the animals close in winter by their opercula, or doors, are known to all. Many snails are not provided with shells, and they secure themselves by creeping under dead leaves, stones, or pieces of wood, or into the sod and the ground.

If we regard the animals in the water we shall find that they are furnished with safeguards as well adapted to their wants as those of their fellows of the air. The larvæ hide, like those of the Ephemerœ, with their whole bodies in the ground, and thus escape destruction by the fish; or they live, like the larvæ of the May-flies, in cases made of splinters of wood, pieces of rush, seeds, bits of shells, or hollow straws and stalks of weeds. Other larvæ conceal themselves in leaf-rollings on the surface of the water or beneath the floating leaves of water-plants The soft animals of the water find their protection in shells of limestone, either spirally coiled or double-valved and kept tightly closed by a strong muscle. Crustaceans are protected by the peculiar armor which gives the class its name, and which they change once a year for a suit of larger size; some members of the family take possession of deserted shells, and concealing their hinder parts within them live thus, and carry their acquired houses about with them, as Diogenes did his tub. The coral-polyps of the ocean build from their secretions solid, branching masses of limestone, within which they conceal their jelly-like forms, furnishing another striking example of the care Nature takes for all its creatures. The boring-worms of the sea, the Serpulæ, and the borers of oyster and other shells, the Sabellœ and the Terchellœ, offer other examples of a similar kind. And the Arenicolœ or sand-worms, like the earth-worms of the land, find their security simply by being under the cover of the sand as they crawl around for their food.—Translated and abridged for the Popular Science Monthly from Die Natur.

 

THE COMET OF 1812 AND 1883.
By Professor DANIEL KIRKWOOD.

IN the quarter of a century included between August, 1802, and August, 1827, Jean Louis Pons discovered thirty comets—twice as many as all observers besides. Of this number are the celebrated comets of short period designated as Encke's, Biela's, and Winnecke's,