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CHAPTER IX 



SPECIAL RELATIONSHIPS AND 



CONTACTS 



THE broad relationships of animals to the world 

 in which they live are often characterized by 

 an extraordinary development of certain special 

 contacts which may become the dominating and con- 

 trolling influences to which all others are more or 

 less subordinated. These special contacts are com- 

 monly overlooked, or at least minimized, and are not 

 considered in their true import and perspective. 



Perhaps the most interesting of these special con- 

 tacts is that having to do with light. Light in some 

 form and in some degree seems to be essential for all 

 animal life. It may well be doubted whether any 

 animal lives in absolute darkness. Those inhabiting 

 deep subterranean streams appear to do so, but the 

 subject has never been investigated. They certainly 

 live in a minimum of light. 



In the deeper portions of the sea there is no light, 

 or at least no effective light. But sea creatures, espe- 

 cially those remaining always beneath the illumi- 

 nated surface layer of water, are remarkable for the 

 luminescence developed in all types save for a few 

 that feed on luminescent organisms. 



This general occurrence of luminescence among the 

 creatures of the sea has never been satisfactorily ex- 

 plained. Luminescence is not known to occur in any 



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