POSSIBLE VALUE OF EYE COLORATION 



the owls do not have the habit. The narrowing of the lids in an emer- 

 gency is open to an utterly different interpretation: it may well be a 

 device for momentarily sharpening vision to a maximum, by employing 

 the lid opening as a stenopaic slit. Myopic humans do the same trick — 

 indeed, the very word 'myopia' is derived from roots which mean 'to shut 

 the eye'. 



Related to the above matter is another claim of the enthusiasts: that 

 the best cases of eye camouflage, by masks and stripes, are seen in lidless 

 vertebrates. Pterois is lidless; but Chrysemys is not. But this and othet 

 turtles, Triturus torosus, fishes, and snakes do have something in com- 

 mon to which attention has not been called. The eyes of aquatic fomis, 

 lidless or not, have no glisten when under water; and the snake spectacle 



Fig. 160 — Coincident disruptive coloration of the iris, conjunrtiva, lids 

 and surrounding skin. 



a, head of a lionfish, Pterois voUtans. After Cott. 

 Chrysemys picta marginata; drawn from life. 



b, head of the western painted turtle, 



is SO quickly dulled after a shed that the snake eye seldom has the luster 

 of that of a bird or mammal. It may not be lidlessness as such, but the 

 absence of glisten, which has made it worth-while for these particular 

 vertebrates to devise camouflage for their eyes. 



Glistening eyes, on the other hand, simply cannot be successfully con- 

 cealed. It almost seems as though the birds and lizards, realizing this, 

 have gone to the other extreme and have deliberately used the eye as the 

 centerpiece of their fanciest decorations. Consider the guano cormorant, 

 Phalacrocorax bougainvillii — it has a sober brown iris, but the naked 

 skin around the eye bears a green ring next the eye, and a red ring out- 



