230 FOUNDERS OF OCEANOGRAPHY 



luminescence in marine organisms may be regarded as an 

 evolutionary series. Starting with the emission of light 

 from a single cell as a non-utilitarian incident of the meta- 

 boUsm of the living protoplasm, we may imagine this vital 

 characteristic becoming of survival value in some sets of 

 organisms and not in others, according to the difference of 

 environment and habits. Furthermore, the value of one 

 type of light -production might be greater in one set of animals 

 than that of another type in a different set. Thus super- 

 ficial photogenous tissue, or more deeply seated glands, a 

 more general diffusion, or a concentration in special photo- 

 spheres, might each be of more use in one case than in 

 another under different environmental conditions. Thus 

 we can imagine the gradual evolution through the ages, 

 under the action of variation and natural selection or elimina- 

 tion, of the different kinds of luminescent organs in accord- 

 ance with their survival value in one kind of animal or 

 another — and thus the diversity of the light-producing organs 

 and their sporadic distribution in the animal kingdom does 

 not seem unnatural. We can, at any rate, imagine a possible 

 explanation of the mystery, and hope that further experi- 

 mental work will throw much needed light upon the real 

 utility of the various types of luminescence. 



