HABITS AND ECONOMY SF THE MOLLUSCA, ll 
their own 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 liying 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 moye- 
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 purple 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 hmpet is commonly overgrown with balani 
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. cochligera) 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 lke 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-preseryation, the 
escape from danger, and the choice of food. An instance of 
something like social feeling has been obseryed in a Roman 
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 Roberts, of Lyme Regis, 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 food 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 that have been given for rare shells are less to be regretted, 
