CH. VI MAEINE FAUNA OF TALIS8E 8E0BES 149 



brilliant colours which so many of them display. It is not 

 sufficient, in these days, simply to state as a fact that cer- 

 tain animals or plants possess certain colours, but it is 

 necessary, if possible, to discover the meaning of the colours 

 and the part they play in the economy of the individual or 

 in the struggle for existence of the species. 



Colours and colouring substances perform various 

 functions in the animal and vegetable kingdoms. Some- 

 times the colours of animals serve to attract, sometimes to 

 repel, sometimes they are merely signs of disease or weak- 

 ness. Some colouring matters, again, perform important 

 physiological functions such as the haemoglobin of the blood, 

 others are signs that a chemical or physiological change in 

 certain substances has taken place. It is not necessary for 

 me to run through here all the various meanings of colour 

 in the animal kingdom, suffice it to say that the colour of 

 corals has probably a physiological meaning and is intimately 

 connected with some chemical change constantly taking 

 place in the coral organisms. 



The only other alternative to this would be that it is use- 

 ful as a protection against enemies, but it is impossible to 

 see how the colours of any of the corals can act in this way. 

 The enemies of the corals, such as the reef j&shes which are 

 said to browse upon them, would be attracted rather than 

 repelled or deceived by the bright colours of the young grow- 

 ing points of the Zoantharia or the plumed tentacles of the 

 Alcyonaria. 



If we admit, and I think we must, that the colours have 

 a physiological function, we have two, and as far as our 

 knowledge goes at present only two, alternatives before us. 

 They may either be respiratory in function or of the nature 

 of the green colouring matter in plants assimilating carbonic 

 acid from the water for purposes of nutrition. I do not 

 deny that many of the colouring matters in corals may be 



