HOW ANIMALS ADAPT THEMSELVES 17 



shell and animal, therefore, are at first nearly 

 transparent, but in older life both become more 

 opaque; the blue stripes, too, are almost or quite 

 obliterated in the after-growth of the shell, slight 

 traces of them alone remaining at its apex. This 

 change of colour fits the animal for the new home 

 in which it settles, for it moves down from the 

 leaf of the tangle to its root, and there finds a 

 snug shelter among the coral-shaped branches of 

 which the root is composed. Not many reflec- 

 tions of the blue sky are likely to reach the 

 recesses of the tangle-root, so the creature has 

 no longer any need of its protective colouring 

 of blue. 



The adult shell, however, retains a certain de- 

 gree of translucency, which matches very well 

 with the colouring of the tangle-root; and thus 

 presents a great contrast to the shell of the com- 

 mon Limpet, which is found on rocks. The rug- 

 ged surface of the latter is usually more or less 

 irregularly speckled in harmony with the sur- 

 faces on which it lives, though this shell also 

 presents when young occasional touches of blue, 

 which suggests a family likeness in colour tastes 

 on the part of the two kinds of Limpet. The 

 blue in this case, however, is of the dullest and 

 dingiest shade. The Patella pellucida is common 

 on the more rocky portions of our coasts; in 

 spring the young may be seen in thousands on 

 the seaweeds of the Isle of Man ; here its habits 

 were first observed and described in detail by 

 the Manx naturalist Forbes, who noticed its pe- 

 culiar way of finding a hiding place among the 

 roots of the tangle. The same shell-fish, in con- 

 trast with the commoner Limpet of the rocks, 

 affords another instance of the way in which 



