64 ANIMAL COLOKATIOF. 



of a grub" (Andrew Murray, " Disguises of Nature," p. 9). 

 Here light may have been influential in distinguishing the two 

 halves of the body. 



Bright Colours in Subterranean Animals. 



Absence of light seems to have had no effect in the case of 

 mammalia which habitually live below the surface of the soil, 

 nor in earthworms or snakes which live underground. 



Uropeltid snakes {Rhinophis oxyrhynchus), which live "deep 

 in the ground," and have degenerate eyes, are nevertheless 



often marked with brilliant red and yellow colours. 



* 



Influence of Light upon Colours of Flat Fish. 



It has been supposed that flat fish, which habitually rest 

 upon one side, are examples of the modifications of colour 

 which have been caused by natural selection ; the exposed side 

 is coloured, — protectively coloured and variable (see p. 140), 

 while the underside is white. In the young of these fishes, 

 which are symmetrical and swim in the position of a roach or 

 perch, both sides are coloured alike. When the asymmetry 

 has been acquired, and the fish has come to lie upon one side, 

 it is believed that the pigment has disappeared from that side, 

 on account of its uselessness. This explanation has an air of 

 reasonableness, which might lead to the inference that it had 

 been amply tested by actual experiment. 



Mr. Cunniilgham, naturalist to the Marine Biological 

 Association, has made an interesting series of experiments with 

 a view to testing the validity of this explanation. The fish 

 used for their experiments were young flounders.* After 

 keeping the fish in tanks with a mirror at the bottom, the 

 usually white under-surface was found in several cases to 

 be largely pigmented, which seems to show that some environ- 

 * Zoologischer Anzru/r>r, Feb. 1891. 



