HAEITS AND ECONOMY OF THE MOLLUSCA. 15 



fully on sea-weed, or subsist on the nutrient particles which the 

 sea itself brings to their mouths ; the rest browse on living zoo- 

 phytes, 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 ex- 

 pressly given to compensate for the slowness of their movement, 

 and the dimness of theii' 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 concealment for their 

 safety. It has been frequently remarked that molluscs resemble 

 the h*ue and appearance of the situation they frequent ; thus, the 

 limpet is commonly overgi'own with halani 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. cocJdigera) coats itself with shell-sand, and the 

 camer-trochus cements shells and corals to the margin of its 

 habitation, or so loads it with pebbles, that it looks but like a 

 little heap of stones. 



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

 a low order, being almost Kmited to self-preservation, the escape 

 from danger, and the choice of food. Their history offers none 

 of those marvels which the entomologist loves to relate. An 

 instance of something like social feeling has been observed in a 

 Koman snail (helix jjomatia) who, after escaping from a garden, 

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

 plished naturalist who witnessed the cii'cumstance hesitated to 

 record a thing so unexampled. The limpet, too, if we may trust 

 the observations of Mr. llobert, 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 immortalized the sagacity of the razor-fish, who sub- 

 mits to be salted in his hole, rather than expose himself to be 

 caught, after finding that the enemy is lying in wait for him. 



