EXTERNAL ANATOMY. EYES. 
4 S 
colours. In the 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 rangeof our projected inquiry, butwhich more strictly 
belong to the province of the comparative anatomist. 
We shall, therefore, merely endeavour to generahse 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 otlier, are nota- 
ble examples; those of the falcons are not very much 
smaUer; but, among the goatsuckers, they are enormous. 
Next to these, as a family, we may mention the plovers, 
particularly the genus (Edivnemus ; 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 Caprimulyus has 
hitherto been found, having other than entirely black 
eyes ; these organs again, are equally large among the 
woodcocks and snipes, which arc, 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 pecuharity 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; th^ 
organs are disproportionately small in the majority of the 
