GOLDEN EAGLE. 11 



Dr. Fleming, who had opportunities of observing these 

 birds when residing in Zetland, says that they are general de- 

 predators, and in the breeding-season rob the rock birds of 

 their young, especially the Gulls and Cormorants. This 

 habit is probably common to both species of British Eagles. 



The power of vision in birds is observed to be very extra- 

 ordinary ; and in none is it more conspicuous than in the 

 Eagles, and the Falconida generally. It has been stated 

 that probably in the whole range of anatomical structure, 

 no more perfect or more conclusive proofs of design could 

 be adduced than are to be found in the numerous and beau- 

 tiful modifications in the form of various parts of the eyes 

 of different animals, destined to exercise vision in media 

 of various degrees of transparency as well as density. The 

 figure on the right hand of the vignette at the end of this 

 article represents the circle, composed of fifteen bony plates, 

 by which the orb of the eye of the Golden Eagle is sup- 

 ported. These bony plates are capable of slight motion 

 upon each other. The figure on the left hand in the vi- 

 gnette represents the crystalline lens of the same bird ; the 

 lens being subject to great variety of form in different birds. 

 In the Eagle, the proportion of the axis to the diameter of 

 the lens is as three and eight-tenths to five and seven-tenths ; 

 in the Great Owl, which seeks its prey at twilight, the re- 

 lative proportions of the lens are as six and five-tenths to 

 seven and eight- tenths ; and in the Swan, which has to select 

 its food under water, the proportions of the lens are as 

 three to three and eight-tenths. Birds have also the power 

 of altering the degree of the convexity of the cornea. With 

 numerous modifications of form, aided by delicate muscular 

 arrangement, birds appear to have the power of obtaining 

 such variable degrees of extent or intensity of vision as are 

 most in accordance with their peculiar habits and necessities. 



