Variation and Natui^al Selection. 83 



from being the subject of unpleasant experiments in the 

 matter. Other caterpillars, like the palmer-worms, are 

 protected by barbed hairs that are intensely irritating. 

 They, too, can afford to be conspicuous. But a sweet and 

 edible caterpillar, if conspicuous, is eaten, and thus by the 

 elimination of the conspicuous the numerous dull green or 

 brown larvae have survived. 



A walk through the Bird Gallery in the National 

 collection will afford examples of protective resemblance 

 among birds. Look, for example, at the Kentish plover 

 with its eggs and young — faithfully reproduced in our 

 frontispiece — and the way in which the creature is thus 

 protected in early stages of its life will be evident. The 

 stone-curlew, the ptarmigan, and other birds illustrate the 

 same fact, which is also seen with equal clearness in many 

 mammals, the hare being a familiar example. 



Many oceanic organisms are protected through general 

 resemblance. Some, like certain medusae, are transparent. 

 The pellucid or transparent sole of the Pacific {Acliirus 

 peUiicidus), a little fish about three inches long, is so trans- 

 parent that sand and seaweed can be seen distinctly 

 through its tissues. The salpa is transparent save for the 

 intestine and digestive gland, which are brown, and look 

 like shreds of seaweed. Other forms, like the physalia, 

 are caerulean blue. The exposed parts of flat-fish are 

 brown and sandy coloured or speckled like the sea-bottom ; 

 and in some the sand-grains seem to adhere to the skin. 

 So, too, with other fish. " hooking doivn on the dark back 

 of a fish," says Mr. A. E. Wallace, '* it is almost invisible, 

 while to an enemy looking up from below, the light under 

 surface would be equally invisible against the light of 

 clouds and sky." Even some of the most brilliant and 

 gaudiest fish, such as the coral-fish (Chcetodon, Platyglossus, 

 and others), are brightly coloured in accordance with the 

 beautiful tints of the coral-reefs which form their habitat ; 

 the bright-green tints of some tropical forest birds being 

 of like import. No conception of the range of protective 

 resemblance can be formed when the creatures are seen 



