THE EYE AS A WHOLE 



173 



be relatively large in, say, small birds and yet relatively small in such an 

 animal as the horse. Though the horse has larger eyes than any other 

 land mammal, there is ample room for even such large eyes in the head. 

 The small bird must give over a far greater proportion of the head to the 

 eyes if they are to be large enough in actual measurement. 



NOCTURNAL: 

 5 



ARHYTHMIC: 



DIURNAL- 



Fig. 71 — Intraocular proportions in relation to intensity habits. 

 Redrawn from various sources. 



inferior side of eyeball; n- nasal side; s- superior side; /- temporal side. 



Another factor which, by operating upon actual ocular size, has its 

 effect upon relative ocular size, is locomotor speed. Great speed demands 

 high resolving power for better perception of movements and for the 

 avoidance of collisions (Chapter 10, section E) ; and this calls for a large 



