NOTE-BOOK OF A NATURALIST. 231 



white, to prevent detection among tlie snows of tliose 

 inclement regions. 



If we turn to the waters, the same design is evident. 

 Frogs even vary their colour according to that of the 

 mud or sand that forms the bottom of the ponds or 

 streams which they frequent, — nay, the tree-frog (Hyla 

 viridis) takes its specific name from the colour, which 

 renders it so difficult to see it among the leaves, where 

 it adheres by the cupping-glass-like processes at the end 

 of its toes. It is the same with fish, especially those 

 which inhabit the fresh waters. Their backs, with the 

 exception of gold and silver fish, and a few others, are 

 comparatively dark ; and some practice is required before 

 they are satisfactorily made out, as they come like sha- 

 dows, and so depart, under the eye of the spectator. A 

 little boy once called out to a friend to ' come and see, 

 for the bottom of the brook was moving along.' The 

 friend came, and saw that a thick shoal of gudgeons, and 

 roach, and dace, was passing. It is difficult to detect 

 ' the ravenous luce,' as old Izaak calls the pike, with its 

 dark green and mottled back and sides, from the simi- 

 larly-tinted weeds among which that fresh-water shark 

 lies at the watch, as motionless as they. Even when a 

 tearing old trout, a six or seven-pounder, sails, in his 

 wantonness, leisurely up-stream, with his back-fin partly 

 above the surface, on the look-out for a fly, few, except 

 a well-entered fisherman, can tell what shadowy form it 

 is that ripples the wimpling water. But the bellies of 

 fish are white, or nearly so ; thus imitating in a degree 

 the colour of the sky, to deceive the otter, which gene- 

 rally takes its prey from below, swimming under the in- 

 tended victim. Nor is this design less manifest in the 

 colour and appearance of some of the largest terrestrial 

 animals ; for the same principle seems to be kept in 

 view, whether regard be had to the smallest insects, or 

 the quadrupedal giants of the land. 



