IOWA ACADEMY OP SCIENCES. 
33 
Second.— green-light theory of Verrill. This is an 
attempt to explain brilliant coloration as protective.* He 
says in effect 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: f 
‘‘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, i. 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 deep-sea animals. 
(a) Brilliant colors are common in all groups. 
* Report of Commission of Fish and Fisheries, 1883, p. 1054, et seq. 
+ “ Three Cruises of the Blake,” p. 305. 
3 
