SHELLS AND MOLLUSCOUS ANIMALS. 179 



back. It is a pretty shell, clear and brittle, of a 

 white colour, tinged with pale blue. The food of 

 the barnacle consists of small crustaceous or mol- 

 luscous animals ; and at times, when it is actively 

 engaged in catching its prey, we may see pro- 

 truding from its shell, its six pairs of arms, many- 

 jointed and delicately fringed. They are most 

 vigorous animals, and of so sensitive a touch that 

 they can lay hold of the minutest object, and, 

 entangling it in their feather-like arms, they can 

 draw it to the mouth, seize, and devour it. 



Very curious transformations occur in the con- 

 dition of the barnacle tribe during their brief lives. 

 Seeing them as we do, fastened to the timber or 

 the rock, or encrusting the oyster-shell, shut up in 

 their little dwellings, and without any eyes, one 

 would not imagine that they were, at an earlier 

 stage of their existence, endowed with active facul- 

 ties. When first emerging from the egg these 

 animals have a large pair of limbs, provided with 

 hooks, which they are not slow to use when they 

 choose to fasten themselves to any objects ; then 

 they have six pairs of swimming limbs and a jointed 

 tail, the limbs acting like oars, and the tail also 

 serving them as a means of motion, so that 

 they are among the most active creatures of 

 the sea. Their bodies, too, are at this period of 

 their history covered with a shell of the na- 

 ture of that of the crab, and they have large 

 eyes set on stalks. In the course of time the 

 limbs become changed into the fringed arms, and 

 the shelly crust becomes a regularly valved shell ; 

 the stalk in some of the species develops itself, or 

 the cone arises from the wood, or shell, or rocky 

 base. The whole animal is so different when 

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