138 A NATUBALI8T IN CELEBES ch. vi 



white coral sand covered with a sparse vegetation of green 

 weeds. When covered with water this has a uniformly 

 greenish-grey colour. If it were asked why it is that 

 these fishes unconsciously imitate the colour of the sea- 

 bottom, the answer would be that the lagoon is the 

 favourite fishing ground of the fish eagles and hawks, 

 and any fish that were not so coloured would be most 

 obvious to these enemies and be the first to be devoured. 

 The lagoon fishes have, however, many other enemies : 

 large sharks and other voracious fishes often dart across 

 the reef to snatch a hasty meal and retreat again, but it is 

 rather difficult to imagine the colour that would be protective 

 against such enemies as these. Man can probably form a 

 tolerably accurate idea of what colours look like to any 

 other air-breathing animals such as birds, but I doubt 

 whether he can form any idea of the powers of vision of 

 aquatic animals. If a man opens his eyes under water he 

 can see scarcely any distance m front of him. His vision 

 must be vastly inferior in that element to that of fishes, 

 and consequently, I think, we are justified in saying that we 

 can know nothing accurately of the way in which fish are 

 protected from fish enemies by their colour. 



We know that many of our shore and river fishes in 

 England are very differently coloured on their dorsal side 

 and on their ventral side. They present, in fact, one colour 

 to the enemy who approaches them from above, and another 

 to the enemy who approaches them from below. How far 

 this latter colour is one of protective imitation we have no 

 means of knowing until we are better acquainted with the 

 powers of vision of fishes. 



Besides fishes there are but few objects of interest for 

 the naturalist in the lagoon. A small variety of the bright- 

 green zostera and a few corallines are usually the only 

 seaweeds that grow there, and animals are few and far 



