IOWA ACADEMY OF SCIENCES. 33 



Second. — The green-light theory of Verrill. This is an 

 attempt to explain brilliant coloration as protective.* He 

 says in eifect that sunlight penetrates to even the greatest 

 depths and that only green rays reach those regions. He 

 calls attention to the fact that the reds are the predominant, 

 conspicuous colors in deep-sea forms and concludes that in a 

 green light red would be invisible and thus the color would be 

 protective. 



Two objections present themselves to this theory. In the 

 first place, it is incredible that a sufficient amount of sunlight 

 penetrates to great depths to render protective coloration 

 necessary. 



Agassiz, whose knowledge of the deep sea is unsurpassed, 

 says: t 



"We may imagine a reddish, yellow twilight at a depth of 

 about fifty fathoms, passing into a darker region near the 100 

 fathom line; and finally, at 200 fathoms, a district where the 

 light is possibly that of a brilliant star-light night. " 



Now, when we remember how little of color can be seen in 

 the most brilliant moonlight, and how soon all colors but 

 white, if that be a color, are rendered undistinguishable at the 

 approach of dusk in the evening, it becomes evident that our 

 credulity cannot meet the requirement of this theory, /. e. , that 

 green rays penetrate even to 2,000 fathoms or more in such 

 quantities that protective coloration is needed. Again, even if 

 it should prove that light does thus penetrate, animals would 

 be equally well protected by neutral tints without the lavish 

 expenditure of pigment which is so conspicuous among deep- 

 sea forms. 



The third and last theory regards the presence of bright 

 colors and of functional eyes in so many groups as conclusive 

 evidence that light is present in the abysses of the ocean, but 

 considers that the widely diffused phosphorescent light, and 

 not sunlight, is the aid to vision. This theory was adopted by 

 Dr. W. B. Carpenter and Sir Wyville Thomson, and is the 

 view which the present writer regards as the most reasonable. 



Let us briefly recapitulate the facts which are important in 

 this discussion: 

 I. As to coloration of dee})- sea animals. 



(a) Brilliant colors are common in all groups. 



* Report of Commission'of Pish aadJFisheries, 1882, p. 1054, et seq. 

 + " Three.Oruises of the Blake," p. 305. 



