BIRDS 



399 



for lieat -insula! ion and their eyes, highly myopic on land, are entirely adapted 

 for aquatic vision (Fig. 486).^ 



Among the Vertebrates, Birds share with Mammals the distinction 

 of having attained the liighest degree of speeiaHzation, being inferior 

 to them only in cerebral organization. With their intense activity and 

 highly developed emotional life, it would be expected that the 

 visual organs of the former would be very efficient ; this is indeed 

 the case and, in fact, the eyes of Birds are supreme amongst all 



Figs. 487 to 491. — The Eyes of Typical Birds. 



Fig. 487.-^The falcon. 



Fig. 488.— The ow 



Fig. 489.— The parrot. 



Fig. 490. — The ostrich. 



Fig. 491.^The swan. 



Some of Soeininerriiig's heautiful eiigra\'ings. Xatural size, showing the 

 inferior half of a horizontal section of the left eye in eacli case. 



1 Other water-hirds have eyes suited for aerial vision and have adopted devices 

 for adaptation to acjuatic vision, such as an exceptional range of accommodation 

 (cormorant), a highly refractile nictitating membrane (ducks) or the use of a temporal 

 fovea with a hypermetropic refraction (kingfishers) ; others have not done so and act 

 blindly under water (tern) (compare p. 6.14). 



