No. 530] THE PHOTOGENIC FUNCTION 



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presents other difficulties. It is not, however, necessary 

 to the faculty of perception of light that definite organs 

 should exist. It is a quite well-known fact that certain 

 worms, bacteria, and other low organisms are able to 

 detect ultra-violet rays to which the human organism is 

 wholly without sensible response, and yet these actino- 

 tropic (if a coined word may be pardoned) forms show 

 no definite organs such as might be adapted to the receiv- 

 ing and recording of the very short wave-lengths of ultra- 

 violet light. If, then, existing organisms are known to be 

 affected by ultra-violet rays for which they have no 

 special sense-organs, it is certainly logical to assume that 

 they and other forms may also be susceptible to the 

 longer and more easily discerned wave-lengths of visible 

 light — especially when those wave-lengths comprise 

 mainly the rays possessing the highest illuminating effect 

 — and without the necessity for the existence of "eyes" 

 or other definite light-receiving organs. As a matter of 

 fact Noctihica, and numerous other marine organisms 

 have been shown to be susceptible to light, although 

 they possess no specific organs for this function so far as 

 we have been able to make out. 



Another consideration as to the purpose of the light 

 presents itself here. We must consider the nature of the 

 medium in which these creatures live. Water does not 

 lend itself as readily as does air to the diffusion of the 

 particles which produce the sensation of smell ; and hence 

 while odors, or speaking more properly, from the stand- 

 point of marine organisms, flavors or tastes undoubtedly 

 exist in the ocean water, they could not, on account of the 

 water currents, lack of diffusion, etc., serve the purpose 

 which the odors of land animals serve of giving indication 

 of the presence and location of the creatures. It there- 

 fore would not be unreasonable to assume that in the gre- 

 garious simple luminous marine forms, the photogenic 

 function takes the place to some extent of the animal 

 odors of land forms. 



To sum up, then: 



