488 THE POPULAR SCIENCE MONTHLY. 



ferent butterflies resting with their wings folded together on flow- 

 ers, leaves, bark, old walls, dead wood, etc., and to the thousands 

 of instances daily in which insects pass unobserved by being con- 

 founded 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 larvae hide, like those of the Ephemerae, 

 with their whole bodies in the ground, and thus escape destruction by 

 the fish ; or they live, like the larvae 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 larvae 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 masse3 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 Serpulm, and the borers of oyster and other shells, the Sabellm 

 and the Terchellce, offer other examples of a similar kind. And the 

 Arenicola3 y 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 

 arouud for their food. Translated and abridged for the Popular 

 Science Monthly from Die Natur. 







THE COMET OF 1812 AND 1883. 



By Professor DANIEL KIKKWOOD. 



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, 



