322 



ZOOLOGY. 



of prey than in others, leading one to suppose that the sense of 

 smell is acute in this class of birds; and this has been asserted, 

 hut experiments and observations of recent zoologists tend to 

 prove that even in these the prey is detected by the sight, and 

 not by the smell.* The apparatus of hearing is simpler than 

 in mammals. The external ear (figured part of the ear) is 

 wanting, and the apparatus is reduced to an external tube, 

 a tympanic cavity, and internal ear.f But the organ of sight 



Fig. 300. Scoter Duck ; Black Duck. 



seems to be more perfect than in mammals. The eyes are 

 larger proportionally, and new parts exist. The retina is 

 thick, and connected by means of a fold passing from the 

 choroid to the capsule of the lens. It has been called pecten, 

 and by some is thought to be a dependence ~ of the retina. 

 The pupil is always round, the cornea large, and the sclerotic 



* As early as 1817, I ascertained, by direct observation, that the South 

 African vulture is solely guided by sight in discovering his prey. K. K. 



t The osfticula auditus are also reduced in number, and much modified. 

 R. K. 



