"HABITS AND ECONOMY OF THE MOLLUSCA. 11 



their ovm nation. Scarcely one-half the shelly tribes graze 

 peacefully on sea- weed, or subsist on the nutrient particles 

 which the sea itself brings to their mouths ; the rest browse 

 on living zoophytes, or prey upon the vegetable-feeders. 



Yet in no class is the instinct of '* self-preservation" stronger, 

 nor the means of defence more adequate ; their shells seem 

 expressly given to compensate for the slowness of their move- 

 ment, and the dimness of their senses. The cuttle-fish escapes 

 from attack by swimming backwards and beclouding the water 

 with an inky discharge ; and the sea-hare {aplysia) pours out, 

 when irritated, a copious pui'ple fluid, formerly held to be 

 poisonous. Others rely on passive resistance, or on conceal- 

 ment, for their safety. It has been frequently remarked that 

 molluscs resemble the hue and appearance of the situation they 

 frequent ; thus, the limpet is commonly overgrown with haJani 

 and sea-weed, and the ascidian with zoophytes, which form an 

 effectual disguise ; the lima and modiola spin together a screen 

 of grotto-work. One ascidian (a. cochh'aera) coats itself with, 

 shell-sand, and the carrier-trochus cements shells and corals to 

 the margin of its habitation, or so loads it with pebbles, that 

 it looks like a little heap of stones. 



It must be confessed that the instincts of the shell-fish are 

 of a low order, being almost limited to self-preservation, the 

 escape from danger, and the choice of food. An instance of 

 something like social feeling has been observed in a Eoman 

 snail {helix pomatia), who, after escaping from a garden, re- 

 turned to it in quest of his fellow-prisoner ; — but the accom- 

 plished naturalist who witnessed the circumstance hesitated to 

 record a thing so unexampled. The limpet, too, we learn from 

 the observations of Mr. George Eoberts, of Lyme Eegis, is fond 

 of home, or at least possesses a knowledge of topography, and 

 returns to the same roost after an excursion with each tide. 

 Professor Forbes has immortalised the sagacity of the razor- 

 fish, who submits to be salted in his hole, rather than expose 

 himself to be caught, after finding that the enemy is lying in 

 wait for him. On the other hand, Mr. Bowerbank has a curious 

 example of "instinct at fault," in the fossil spine of a sea- 

 urchin, which appears to have been drilled by a carnivorous 

 gasteropod. 



We have spoken of shell-fish as articles of f"'^'^ but they have 

 other uses, even to man ; they are the toys of children, who 

 hear in them the roaring of the sea ; they are the pride of 

 " collectors " — whose wealth is in a cone or " wentle-trap ; " * 



* The extravagant prices tliat have been given for rare shells are less to be regretted, 



