34 IOWA ACADEMY OF SCIENCES. 



(b) Reds, yellows and greens predominate. 



(c) These colors are in masses, usually in striking con- 



trast. 



(d) Commensal associations of similarly and brilliantly 



colored animals are frequent. 



II. As to phiisicdl conditions: 



(a) Great pressure. 



(h) Uniform low temperature. 



(c) Practical absence of sunlight. 



(d) Aggregation of animals in limited areas. 



(e) A considerable amount of organic matter near the 



bottom. 



III. As to cisual organs (unong deep-sea animals: 



(a) They are possessed by a majority of animals that 

 normally possess them in shallow water. 



(Jj) They are often of great size among deep-sea forms. 



(c) They are often, on the other hand, either rudimentary 

 or aborted. 



IV. ^6- to phosphorescent light: 



(a) It is found among practically all classes of deep-sea 



forms. 



(b) It is often of remarkable brilliancy. I, myself, have 



seen it so brilliant, on the surface of course, that 

 ordinary print could be read from the deck of a 

 vessel. 



(c) It is possessed by animals that are known to be aggre- 



gated in immense quantities at certain spots at the 

 sea bottom. 



(d) It has the remarkable actinic property of rendering 



particularly conspicuous the reds, yellows and 



greens.* 

 Here, then, it would seem that we have a light that would 

 render the characteristic colors of deep-sea animals, /. e., the 

 reds, yellows and greens, conspicuous, and no less nor more 

 explicable than similar colors among their shallow- water rela- 

 tives. In many cases they are doubtless to be regarded as 

 warning coloration, as in the sea urchins, whose sharp spines 

 are frequently banded with brilliantly contrasted red and 



*Mosely found that the phosphorescent light emitted by certain marine forms 

 consisted of red, yellow and green rays only, and adds: "Hence, were the light in the 

 deep sea derived from this source, in the absence of blue and violet, only red, yellow 

 and green colors could be effective." (Quoted from Agassi/.' "Three Cruises of the 

 Blake," p. 310.) 



