24 FACULTIES OF BIRDS. 



M. Vaillant mentions a similar circumstance which he 

 more than once observed in different species of owls, 

 if they chanced to be roused from their lurking 

 places by day, when instead of pursuing- small birds, 

 which are their natural prey, they fled from them in 

 fear *. 



Wilson says of the snowy owl (Stryx nyctea) that 

 " the conformation of the eye forms a curious and 

 interesting subject to the young anatomist. The 

 globe of the eye is immoveably fixed in its socket 

 by a strong, elastic, hard, cartilaginous case, in form of 

 a truncated cone : this case being closely covered with 

 a skin appears at first to be of one continued piece ; 

 but on removing the exterior membrane it is found 

 to be formed of fifteen pieces, placed like the staves 

 of a cask, overlapping a little at the base or narrow 

 end, and seem as if capable of being enlarged or 

 contracted, perhaps by the muscular membrane in 

 which they are encased." " In five other different 

 species of owls," adds Wilson, " which I have since 

 examined, I found nearly the same conformation of 

 this organ, and exactly the same number of staves. 

 The eye being thus fixed, these birds, as they view 

 different objects, are always obliged to turn the 

 head ; and nature has so excellently adapted their 

 neck to this purpose, that they can with ease turn it 

 round, without moving the body, in almost a complete 

 circlet." 



In nocturnal birds, M. de Blainville remarks that 

 the eye, besides being comparatively very large, is 

 flat (comprime) both before and behind, while the 

 transparent cornea is placed at the end of a sort of 

 tube formed by the bony portion of the sclerotic. 

 The retina is consequently comparatively very large 

 and extended, and the iris also; while the mem- 



* Oiseaux d'Afrique, torn. i. 

 t Amer, Ornith, iv. 56, 1st edit. 



