HOW ANIMALS ADAPT THEMSELVES 15 



up as a clerk, and he will lose much of his sturdi- 

 ness. Let the mountaineer's grandsons be 

 brought up as cobblers, and by the time they 

 are thirty they will not be remarkable for their 

 muscular capabilities. 



Just in a similar way the bodies of animals 

 adapt themselves to circumstances. It is not 

 always possible to trace the steps by which this 

 has been done. But sometimes it is so; and we 

 may find a whole series of varieties that are plain- 

 ly due to adaptation. When we see an animal 

 which is in some way especially fitted for its sur- 

 roundings, we are therefore justified in conclud- 

 ing that it has become so by degrees. 



The way in which animals adapt themselves 

 to their surroundings in the matter of colour 

 would afford material for several volumes each 

 as large as this one. Those who have not trav- 

 elled in foreign countries may perhaps find it dif- 

 ficult to realise that brilliant colouring and showy 

 patterns can ever enable an animal to hide itself 

 successfully. But an instance may be taken from 

 an animal common on our own shores which will 

 illustrate how this principle works. 



In the spring there may be found in large 

 numbers upon our rocky coasts a little oval shell- 

 fish, about one-third of an inch long, sticking to 

 the fronds of the tangle and other broad-leaved 

 seaweeds. The animal is of a very pale brown 

 colour; its shell brownish and semi-transparent, 

 with several stripes of brilliant turquoise blue 

 down the back. These stripes are not continu- 

 ous, but interrupted at intervals so as to give 

 them a beady look. Taken in the hand and looked 

 at closely, the shell, with its contrast of blue 

 stripes on a brown ground, is extremely conspic- 



