THE LITTORAL AND MARINE FAUNA 327 



very fine fish may be sliot as they bolt across a shallow pool 

 to the deeper water beyond. These barrier pools are the homes 

 of some of the most wonderful of all the atoll fish, and it is 

 impossible to describe the splendid colom'ing, vivid blue and 

 intense purple, of the myriad tiny fish that spend their lives 

 among the branching growths of coral. The Pig-fish {Balistes) 

 and a host of others have wonderful patterns picked out in 

 boldly contrasted colours, and there are many very curious 

 points in connection with the mode of coloration of these 

 bright tropical fish. 



It is not uncommon for the two ends of a fish to be 

 entirely different in coloration and pattern, so that an appear- 

 ance is presented as though two fish had been cut in half, 

 and the head end of one joined to the tail end of the other. 

 Another very common design is for a fish to possess one patch 

 of colour that presents a glaring contrast to all the rest of its 

 body ; and in such a case a vivid spot is seen moving through 

 the water as the fish swims, but the whole body of the creature 

 becomes very difficult to define. 



There is no doubt that these strange freaks of coloration 

 serve a very definite purpose, but we know so little of the 

 elements that enter into the factors of the lives of these 

 fish, and so little of the appearance that these things present 

 when viewed by other creatures in the water, that they appear 

 to us rather as strange and fantastic efforts of Nature than 

 as the useful defensive and offensive aids that they un- 

 doubtedly are. There is much to be learned about these 

 creatures, and no better place than Cocos-Keeling could be 

 chosen for studying the reasons for their strange ornamenta- 

 tions, for, in the clear water of the barrier pools and in the 

 lagoon, observations may be made upon them in their natural 

 environment under the very best conditions. 



Strange methods of defence of more obvious utility than 

 coloration are to be seen in the many fantastic forms of fish 

 which carry armour-plate, and spikes around their bodies. The 

 Tetradonts show some of these modifications in their most 

 exaggerated forms, as some are shaped like little hard boxes 



