SEEN WITH THE EYE OF A FISH 35 



limpid brook and gurgling stream from the Malay 

 Archipelago to the West Coast of Ireland. Probably the 

 loach depends for his survival over so wide a distribution 

 on exceptional powers of adapting his markings to new 

 surroundings. As an illustration of the usual markings 

 on a stone loach, look at the middle photograph on 

 the plate that precedes p. 31. 



Next look at the skins of two loach on the accom- 

 panying plate. The first is a photograph of the skin 

 of a loach caught in a brook where the bottom was 

 muddy ; the second came from the same brook several 

 miles higher up, where the water rippled over gravel. 



In the first the pigment cells have increased in 

 number, and, instead of the usual spotty appearance of 

 the skin, the colour is much more uniform, in order that 

 this fish may the better be concealed on a dark, dirty 

 bottom. In the second the spotty appearance is exag- 

 gerated, and even the back has quite clear spaces upon 

 it an arrangement of pigment that is more suitable to 

 a gravelly bottom. 



In some fish the markings invariably change during 

 the life of an individual. This is so in the pike. The 

 body of the young pike is crossed by several brilliant 

 yellow bars, and lying hidden amongst the reeds these 

 bars protect him in much the same way as the bars 

 protect the perch. He can thus catch his prey and also 

 escape falling a victim to his enemies. 



When the pike is nine inches or more in length, the 

 yellow pigment cells disappear at regular intervals along 



