MOLLUSCA. 757 



while the circumstance of its surface being smooth, or variously grooved, 

 tuberculated, or marked with spines, supplies others. The immense variety 

 in the coloring, also, atTords obvious means of specific distinction. All the 

 mollusca are oviparous. The reproduction is therefore necessarily effected 

 by sexual impregnation. In some of the orders of these animals, the sexes 

 are separate, as in the Sepiaria. These animals, however, do not copulate, 

 but the males shed a fecundating fluid upon the ova deposited by the females. 

 It appears that the other mollusca, such in particular as the Gasteropoda and 

 Trachelipoda, have the two sexes united in the same individual. Of these 

 hermaphrodites, some require a reciprocal copulation, while others appear to 

 fecundate themselves. The ova of the mollusca are not in general hatched 

 until after they have been deposited. Some have a crustaceous covering like 

 the ova of birds and reptiles, as is the case with the helices; others are 

 sometimes surrounded with a sort of jelly, by which they are attached to- 

 gether, as in the planorbes, lymncza:, &c., and others are contained in mem- 

 branous sacs, of very different forms, sometimes solitary, but more commonly 

 in groups ; each of the sacs containing several young individuals, which 

 issue from them alive, with their shell already formed, as is the case with 

 the Buccina, kc. The mollusca are in general aquatic animals. Many 

 species, however, are terrestrial ; and some appear to live almost constantly 

 under ground, such as the testacella, but this is rare. A great number are 

 found on the surface, such as the limaces, helices, &c. ; w^hile some are to a 

 certain degree amphibious, as the lymnacE. By far the greater part, however, 

 live in water, fresh and salt. Of the fresh water kinds, some remain free at 

 the surface of the mud; others adhere to other bodies. Of the latter, the 

 circumstances, in this respect, are considerably varied. Some are found 

 only on the coasts, and are termed littoral species, as the genera patella, turbo, 

 &c. ; others appear to exist only at a distance from the shores, and in deep 

 water, whence they are called pelagic species ; and the Sepiaria wander in 

 the depths of the ocean. With respect to their geographical distribution, 

 little is known, this subject not having been submitted to sufficient investi- 

 gation. They are found, however, in all parts of the world, whether in the 

 seas, rivers, and lakes, or on land. Certain tribes are confined to particular 

 zones, while others appear to inhabit all. Thus the Sepiaria occur in all 

 seas, while the nautilus and spirula are found only in the torrid zone. The 

 food of the mollusca consists of almost all sorts of substances, animal and 

 vegetable, in all states, living or dead, fresh or putrid; but each species is in 

 general confined to a certain kind. The uses of the mollusca, in the econo- 

 my of nature, are varied and extensive. They afford food to numerous 

 animals, especially fishes and birds, and to man himself. The savage tribes 

 which live along the coast, in many parts of the world, employ them much 

 as an article of food. Even in civilized countries, the mollusca frequently 

 form a considerable portion of sustenance, although in general they are nei- 

 ther very pleasant nor wholesome. The cuttle-fish furnishes a fluid from 



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