HABITS AND ECOITOMY OF THE MOLLUSCA . 9 



in abliorreiice, and fast or sliift their quarters wliile that crop is 

 on the ground.* Some, like the " cellar- snail," feed on crypto- 

 gamic vegetation, or on decaying leaves ; and the slugs are 

 attracted by fungi, or any odorous substances. The round- 

 mouthed sea-snails are nearly all vegetarians, and consequently 

 limited to the shore and the shallow waters in which sea-weeds 

 grow. Beyond fifteen fathoms, almost the only vegetable pro- 

 duction is the nullipore ; but here corals and horny zoophytes 

 take the place of algce, and afford a more nutritious diet. 



The whole of the bivalves, and other headless molluscs livo 

 on infusoria, or on microscopic plants, brought to them by the 

 current which their ciliary apparatus perpetually excites ; such, 

 too, must be the sustenance of the magilus, sunk in its coral 

 bed, and of the calyptrcea, fettered to its birth-place by its cal- 

 careous foot. 



The carnivorous tribes prey chiefly on other shell-fish, or on 

 zoophytes ; since, with the exception of the cuttle-fishes, their 

 organisation scarcely adapts them for pursuing and destroying 

 other classes of animals. One remarkable exception is formed 

 by the stili/er, which lives parasitically on the star-fish and sea- 

 urchin ; and another by the tesfaceUa, which j^reys on the 

 common earth-worm, following it in its burrow, and wearing 

 a buckler, which protects it in the rear. 



Most of the siphonated univalves are animal-feeders ; the 

 carrion-eating stromb and whelk consume the fishes and other 

 creatures, whose remains are always plentiful on rough and 

 rocky coasts. Many wage war on their own relatives, and 

 take them by assault ; the bivalves may close,'and the oper- 

 culated nerite retire into his home, but the enemy, with ras]")- 

 like tongue, armed with siliceous teeth, files a hole through 

 the shell, — vain shield where instinct guides the attack ! Of 

 the myriads of small shells which the sea heaps up in every 

 sheltered " ness," a large proportion will be found thus bored 

 by the whelks and purples; and in fossil shell-beds, such as 

 that in the Touraine, nearly half the bivalves and sea- snails 

 are perforated, — the relics of antediluvian banquets. 



This is on the shore, or on the bed of the sea ; far away from 

 land the carinaria and firola pui'sue the floating acalephe; and 

 the argonaut, with his relative the spirula, both carnivorous, 

 are found in the "high seas," in almost every quarter of the 

 globe. The most active and rapacious of all are the calamariea 



• Dilute lime-water and very weak alkaline solutions are more fatal to snails \hsj\ 

 «ven salt. 



B 3 



