Xo. 486] 



THE PROBLEM OF COLOR VISION 



367 



and in the fovea itself only cones are found. These cones, how- 

 ever, are strikingly rod-like in form, and greatly exceed the rods 

 in length (Fig. 1, B). Slender cones are also found in the thick- 

 ened area centralis which in many mammals replaces the human 

 fovea. 



In the ape, horse, pig, cow, sheep, and dog the rods and cones 

 are similar to those of man. In rodents which avoid the light 

 the cones are "very small and hard to detect since their inner 

 segments scarcely differ from those of the rods, from wliich they 

 may be distinguished by their much shorter outer segment. M. 



nu. r.f. Rod, z.s.... as. S,P. 



Schultze at first (piostioned the existence of cones in the mouse, 

 guinea pig, mole, hedgehog, and bat. Tiie cat undoubtedly has 

 cones but they are small, slender, and except in the area, infre- 

 cpient."^ Birds have a single or double fovea, like that of man. 

 Cones are small but very numerous, and in their inner segments 



various sliadcs of yt'Uow. urceu or red. l'n'>\iui;il)ly these drops 



