POSSIBLE VALUE OF EYE COLORATION 545 



The strongly nocturnal oil-bird iSteatornis) has bright blue eyes, and 

 most owls have yellow ones.* Most wild mammals are dark brown or dark 

 gray, and their irides are almost always of some shade of brown — small 

 felids being quite exceptional with their metallic green. Under scotopic 

 conditions, favored by most mammals, it will not matter a particle, for 

 the concealment of the eye, whether the iris matches the body in color or 

 not, so long as the two are roughly matched in tone or albedo. But the 

 same, standard, dark brown mammahan iris occurs also in light gray 



Fig. 158 — "Diagram illustrating the in- 

 herent conspicuousness of an eye-spot, 

 which attracts attention to itself in pref- 

 erence to a variety of other, and even 

 larger, objects in the visual field" (Cott). 



Fig. 159 — Eye-masks. After Cott. 



a, Oxybelis acuminatus. 



b, Rana sphenocephala. 



diurnal monkeys and squirrels — which is reason enough for thinking that 

 the dark iris of a dusky and nocturnal mammal has no standing as an 

 adaptation for concealment. Again, most salamanders have dark brown 

 eyes, yet many of them have gaily colored bodies. 



Among those vertebrates which are much out where other animals can 

 get a good look at them — that is, the diurnal and arhythmic ones — it is 

 highly exceptional for the iris to be unicolor, and a match for the head 



*So also the nortumal bat-eating hawk, Machaerhamphus alcinus. 



