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HABITS AND ECONOMY OF THE MOLLUSCA. 9 
in abhorrence, and fast or shift their quarters while 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 alge, and afford a more nutritious diet. 
The whole of the bivalves, and other headless molluscs live 
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 calyptreea, 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 stilifer, which lives parasitically on the star-fish and sea- 
urchin; and another by the testacella, which preys 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 rasp- 
like tongue, armed with siliceous teeth, files a hole through 
the shell,—vyain 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, suck 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 earinaria and jirola pursue 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 calamaries 
* Dilute lime-water and very weak alkaline solutions are more fatal to snails than 
even salt, 
BS 
