94 THE WONDER OF LIFE 



cean. It is so common that it surely has some significance. 



Perhaps it has different meanings in different animals, 

 and there is no lack of suggestions. May it be sometimes 

 a lure, attracting victims, who come like moths to the 

 candle ? Is it sometimes an advertisement on the part of 

 unpalatable creatures, warning off intruders and molesters, 

 as the rattlesnake does with its rattle 1 Does it some- 

 times serve as a lantern, guiding the active animal to its 

 prey ? Of course that would not apply to cases where 

 the light is at the hind end ! Does it serve in some cases 

 as a ' recognition mark ', enabling those of the same kin 

 to know one another ? In some fishes the disposition of 

 the luminescent organs on the body is different in the two 

 sexes. But phosphorescence, as it is called, remains an 

 unsolved problem. 



Another difficulty is raised by the fact that there is so 

 much colour in Deep-Sea animals. What can be the use of 

 that in an abode of darkness ? There are many reds, e.g. 

 in Crustaceans and Anemones ; there are shades of orange 

 and yellow ; there are some instances of beautiful blue ; 

 there is almost no green. It is noteworthy that there is 

 very httle in the way of spots or stripes, most of the animals 

 being all one colour. It is probable enough that there is 

 no utihtarian interpretation of these Deep-Sea colours, 

 which may be simple by-effects of useful structures and 

 functions. It may be that the Deep-Sea colours are like 

 those in withering leaves — without utiUty in themselves. 



The autumn colouring of withering leaves is largely due 

 to the ebbing vitality, just as floral colouring is largely due 

 to intense vitality. Decomposition products in the former, 

 waste products in the latter may not be chemically far 

 apart. But while the pigmentation of the flowers is turned 



