OCEAN LIFE. 47 



soluble in acid), they can be used like a file for the abrasion of 

 very hard substances. With them the Limpet rasps the stony 

 mullipore, the Whelk bores holes in other shells, and the Cuttle- 

 fish doubtless uses its tongue in the same manner as the cat.' 



"In each transverse row, there is generally a variously-toothed 

 plate, pointing backwards, and overlapping the base of its pre- 

 decessor ; while on each side of this there are several lateral 

 teeth in the form of curved spines which arch inwards. The 

 tongue of the Limpet is longer, when extended, than the whole 

 animal ; that of the Whelk has a hundred rows of teeth, while 

 the great Slug has one hundred and sixty rows, with one hun- 

 dred and eighty teeth in each row. The stomach is sometimes 

 armed with horny plates and teeth, as in the* Sea-hare (Aplysia), 

 which feeds on leathery Fuel. 



" The shell is formed in the same manner as in the CONCHI- 

 FERA, by the folding back of the edge of the mantle. Very 

 many species carry on the hinder part of the body a horny or 

 shelly plate (Opereulum), which accurately closes the aperture 

 of the shell, when the animal has withdrawn into its recesses. 

 The form of this appendage is ordinarily that of a very flat cone, 

 made by successive layers, each a little larger than its predeces- 

 sor, or a flattened spire. The common Top-shells (Trochus,) 

 afford good example of the spiral operculum." 



PISCES. FISHES. 



"To whatever portion of the animal world we turn our attention, 

 we find the lowest and least perfectly organized tribes to be in- 

 habitants of the water. To dwell upon land, necessarily demands 

 no inconsiderable share of strength and activity, limbs sufficiently 

 strong to support the weight of the body, muscles possessed of 

 great power and energy of action, acute and vigilant organs of 

 sense, and, moreover, intelligence and cunning proportioned to 

 the dangers and necessities of terrestrial existence. 



"The inhabitant of the waters, on the contrary, although 

 less highly gifted, may be fully competent to enjoy the position 



