1 82 MOLLUSKS. 



state ; it is only then that they develope their form and true 

 appearance by unfolding their different organs, which in the dead 

 animal are always shrunk, retracted, collapsed, or disfigured to 

 such an extent that there is no possibility of delineating them, 

 insomuch, indeed, that the same individual has again and again 

 been described under various names as belonging to different 

 species. 



When we call to mind the incalculable numbers of these crea- 

 tures that crawl on the bottom or swim in the bosom of the ocean, 

 and that everywhere abound on dry land, it is evident that their 

 .importance in creation must be great beyond human speculation. 

 They are the frequent victims of the indiscriminating and almost 

 insatiable appetite of fishes, and from the stomach of a cod or a 

 flounder many a shell may be procured not otherwise so easily 

 obtainable. They constitute the principal food of innumerable 

 birds and reptiles. They furnish materials valuable in the arts, 

 and many of them are eaten by mankind. 



Various are the forms and widely different the relative perfec- 

 tion of the Mollusks as regards their endowments and capabilities : 

 some, as the Polyzoa, fixed to the surface of foreign bodies, entirely 

 deprived of organs connected with the higher senses, and unable 

 to change their position, are content to protrude at intervals their 

 ciliated arms, and thus entrap such passing prey as suits their 

 appetite. Others, the Brachiopoda, equally incapable of loco- 

 motion, but furnished with arms of different construction, catch 

 their food by an equally curious mechanism. 



The Tunicata, enclosed in leather-like bags, firmly rooted to 

 the rocks or aggregated into singular compound masses, adorn 

 the beach with their kaleidoscope patterns, or float through the 

 ocean at the mercy of the waves. The Conchifera inhabit bivalve 

 shells ; while the Gasteropod Orders, likewise defended in most 

 instances by a shelly covering, creep about by means of a fleshy 

 disk, and thus being endowed with a locomotive apparatus, exhibit 

 senses of proportionate perfection. The Pteropoda swim in 

 myriads through the sea, supported by two fleshy fins ; while the 

 Cephalopoda, the most highly organized of this large division of 

 animated nature, furnished with both eyes and ears, and armed 

 with formidable means of destroying prey, become tyrants of the 

 deep, and gradually conduct us to the most exalted type of 

 animal existence. These different sections, which constitute so 

 many distinct classes into which the Mollusks have been divided 

 by zoologists, may be arranged in accordance with the following 

 tabular view : 



