144 HABITS AND ECONOMY OF THE MOLLUSOA. 



nest of interlaced byssiferous filaments containing fragments of 

 shells, nullipores, etc. (Jeffreys). 



Mimicr}^ or adaptive coloration in the mollusca has been but 

 little studied. Cephalopods are known to change their color to 

 resemble the ground upon which they rest ; and some of the 

 gastropods living upon marine growths vary their colors 

 according to that of their habitation. Lacuna, on the* North 

 Atlantic Coast of the United States, has a shell tinted con- 

 formably to the different species of Laminaria upon which it is 

 found ; and a little red Chiton lives on rocks carpeted with Algae 

 of the same hue (Morse). 



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 Roman snail {Helix 

 pomatia)^ which, after escaping from a garden, returned to it in 

 quest of a fellow-prisoner ; but the accomplished naturalist who 

 witnessed the circumstance hesitated to record a thing so unex- 

 ampled. 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 

 immortalized the sagacity of the razor-fish, which submits to be 

 salted in its hole, rather than expose itself to be caught, after 

 finding that the enemy is lying in wait for it. 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 b}^ a carnivorous gastropod. 



Monstrosities. We have already spoken of the various ab- 

 normal growths of shells ; the unrolling of the spire, the reversal 

 of its direction, etc., and the displacement of the organs caused 

 by this latter frequently-occurring variation : it remains to 

 mention a few of the less frequentl}^ observed instances of mon- 

 strous growth in other parts of the animal than those afl'ected 

 by its shelly covering. Fischer has seen a Subemarginula 

 having two tentacles and two eyes on each side ; and Bert 

 records the case of a Patella in which those organs were doubled 

 on one side only ; bifid or forked tentacles are not rare among 

 the Limnseans. The union of the long tentacles into a single 

 one has been observed in Limax by Forbes and Hanlej^, and in 

 Yitrina by I'Hdpital. Notwithstanding the coalescence of the 

 tentacles, there were two eyes at the extremity. Double mon- 

 sters have been frequently seen in the embryos of Philine aperta: 

 they appear to be formed b}^ the junction of two germs contained 

 in the same shell. 



Duration and Tenacity of Life. Not much is known respecting 

 the individual duration of the shell-fish, thou2:h their length of 



