GENERAL BIOLOGY 673 



blue oceanic species, living in the intense light of the surface, 

 the formation of blue pigment is so vigorous that it exceeds 

 the destruction. Light is thus a very important agent in all 

 these processes, bearing on the formation and transformation of 

 pigment in the bodies of crustaceans, but it is not the only one. 

 Other powers may equally influence the conditions of pigmenta- 

 tion. Experiments thus prove that when subjected to low 

 temperatures blue colour developed in the animals ; this was in 

 my opinion due to the prevention of the destruction of the blue 

 pigment in the tissues, thus causing an accumulation of this 

 pigment." 



I have quoted Dofiein's theory because it opens up very 

 interesting questions for future experimental research, though it 

 hardly explains all the colour adaptations presented by the 

 oceanic animals, for instance the mirror-like forms with dark 

 backs and silvery sides, from intermediate layers, nor does it 

 explain the profuse variation in the Sargasso animals and their 

 peculiar conformity with the various colour-shades of the ocean 

 and of the Sargasso weed. I fail to see any necessity for con- 

 troversy over the two theories, one claiming the colours as due 

 to adaptation serving the purpose of protection, the other 

 explaining them as being due to peculiar processes of assimila- 

 tion. Perhaps the latter theory alone may in many 'cases be 

 sufficient, but may it not possibly signify the very mechanism 

 by the aid of which the organisms adapt themselves in order to 

 obtain protection ? 



A more perfect understanding can only be obtained from 

 an increased knowledge as to the habitats of animals, as to the 

 physical conditions there, and as to their life-history generally. 

 The influence of various physical factors on the animals may be 

 studied by experiment, and several interesting experiments 

 have already been made. Gamble and Keeble, for instance, 

 have proved the variations in colour of Hippolyte varians to 

 correspond to variations in the colours of the surroundings. 

 But the significance of such influences in the life of the animals 

 can in my opinion only be understood by studying the life of the 

 animals in nature. 



Light-Organs 



That many organisms possess the power of emitting light Phosphor- 

 has been known from earliest times. The Norwegian fisher- ^^'^^"^ ^'^^^" 

 men distinguish two kinds of phosphorescence: "dead 

 phosphorescence" and "fish phosphorescence." The "dead 



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