﻿EXTERNAL ANATOMY. EYES. 43 



colours. In the Sifelet of Le Vaillant, the shafts appear 

 equally long, but are altogether destitute of any web. 



(49.) We may now pass unto the Eyes of birds ; or- 

 gans, indeed, which, from being external, come within 

 the range of our projected inquiry, but which more strictly 

 belong to the province of the comparative anatomist. 

 We shall, therefore, merely endeavour to generalise a few 

 facts which may come within the observation of the 

 majority of students. And, first, in regard to the size 

 of the eyes, in which respect there is a considerable dif- 

 ference in particular groups. We find that the largest 

 eyes are possessed, both among quadrupeds and birds, 

 by such species as feed during the night, of which the 

 lemurs in one class, and the owls in the other, are nota- 

 ble examples: those of the falcons are not very much 

 smaller; but, among the goatsuckers, they are enormous. 

 Next to these, as a family, we may mention the plovers, 

 particularly the genus (Edicnemus ; while the corre- 

 sponding group among quadrupeds, the hare and the 

 jerboas, partake of the same peculiarity. It is a fact 

 worth mentioning, but which we must leave the oculist 

 to explain, that no birds, strictly nocturnal, have a 

 coloured iris : exceptions occur, indeed, among the 

 horned owls ; but we believe that no Caprimulgus has 

 hitherto been found, having other than entirely black 

 eyes ; these organs again, are equally large among the 

 woodcocks and snipes, which are, in a great degree, noc- 

 turnal feeders. In passing on to the other extreme, we 

 find that the humming birds, independent of their di- 

 minutive size, have the smallest eyes in the whole class: 

 perhaps this peculiarity may receive some explanation 

 from the fact, that these birds are only in full activity 

 during the most sultry hours of the day, — a time when 

 nearly all others have retired to the shade, as if to avoid 

 the dazzling reflection of a vertical sun. It will be re- 

 membered also, that, in harmony with the small eyes of 

 the tenuirostral tribe, we find the quadrupeds which re- 

 present them are equally remarkable in this respect; these 

 organs are disproportionately small in the majority of the 



