REASON FOR ACCOMMODATION 



251 



Lens At Rest: 



eye not adjusted for distance 

 Lens Moves Backward: 



eye adjusted for distance 



eye not adjusted for near 



Fig. 98 — The 'negative' accommodation of those animals whose eflFort of accommodation 

 moves the lens backward (lampreys; teleosts; probably holosteans). 



Lens At Rest 



eye adjusted for distance 

 Lens Moves Forward: 



eye not adjusted for distance 



eye adjusted for near 



Fig. 99 — ^The 'positive' accommodation of those animals whose effort of accommodation 

 moves the lens forward (elasmobranchs; amphibians; snakes). 



Lens At Rest 



eye adjusted for distance 

 Lens Curvature Sharpens 



eye not adjusted for distance 



eye adjusted for near 



Fig. 100 — The 'positive' accommodation of those animals whose effort of accommodation 

 sharpens the curvature of the lens (reptiles except snakes; birds; mammals). 



