70 



VERTEBRATE PHOTORECEPTORS 



TABLE 2 



Showing Ratios Based upon Comparative Measurements of the 

 Eyes of Nocturnal Lemuroids, Monkeys and Man * 



Galago and Nycticebus are nocturnal lemurs; Nyctipithecus is a nocturnal 

 monkey. 



* Measurements were made from sections selected from the horizontal or vertical meridian, 

 t Based on linear measurements in inches of eye sections at a magnification of X 11. 

 ** Based on planimeter surface area measurements of the various eye structures drawn at 

 a magnification of X 11. 



tt Same as B only at a magnification of X 26. 



Whereas monkeys in general are essentially diurnal in 

 their mode of life, there is one, the platyrrhine monkey, 

 Nyctipithecus, commonly known as the owl monkey, which 

 is strictly nocturnal in its habits. The eye of this animal was 

 described previously by WooUard (1927) and in more detail 

 by the author (1941). 



Although Nyctipithecus is a real monkey, the general 

 features of its eye correspond more closely to those of the 

 nocturnal lemuroids (Galago and Nycticebus) than to those 

 which typify the anthropoid eye. This is not because it is a 

 primitive form, but because the eye is specialized for noc- 

 turnal vision. As is seen in Figure 51 and in Table 2, the 

 cornea presents a marked curvature like that of Nycticebus 

 and occupies about one-third the perimeter of the bulb. 

 This is in contrast with the diurnal marmoset where the 

 cornea constitutes only one-fifth of the perimeter of the 

 globe — a condition similar to that in the human eye. The 

 lens is also relatively large as is the anterior chamber — a 



