THE STRUCTURE OF VISUAL CELLS 



41 



tude as given by Duke-Elder (130,000-140,000) and Oster- 

 berg (147,000). From this it may be safe to say that, in 

 general, there are something of the order of 140,000 cones 

 per sq. mm. at the macula, and that the cones in the human 



Fig. 30. Cones from various vertebrates. A, catfish; B, frog; C, alligator; 

 D, lizard; E, chicken; F, monkey (marmoset); G, rhesus monkey; H, man. 

 (Figures are not drawn to same scale.) a, foveal cone; b, parafoveal cone; 

 c, peripheral cone; n, nucleus; m, myoid; p, paraboloid; e, ellipsoid; o, oil 

 globule; o.s., outer segment. (Figures of visual cells of representative verte- 

 brates drawn to a uniform magnification are given by Arey, 1928, Special 

 Cytology, v. 2, Paul B. Hoeber. New York.) 



eye total about 7,000,000, whereas the rods have been esti- 

 mated as from 75,000,000 to 170,000,000. As one approaches 

 the ora serrata, the cones become gradually shorter and 

 thicker and also less numerous per unit area. This in general 

 is true of all animals. 



