PECULIAR ORGANIZATIONS. 
137 
he may steal upon them unseen. This is a critical distinc¬ 
tion; and is mechanical: but it may be suggested, and I 
think not without probability, that it is the effect of con¬ 
tinued habit. 
The eyes of animals which follow their prey by night, 
as cats, owls, &c. possess a faculty not given to those of 
other species, namely, of closing the pupil entirely. The 
final cause of which seems to be this:—It was necessary 
for such animals to be able to descry objects with very 
small degrees of light. This capacity depended upon the 
superior sensibility of the retina; that is, upon its being 
affected by the most feeble impulses. But that tenderness 
of structure, which rendered the membrane thus exquisite¬ 
ly sensible, rendered it also liable to be offended by the 
access of stronger degrees of light. The contractile range, 
therefore, of the pupil is increased in these animals, so as 
to enable them to close the aperture entirely: which in¬ 
cludes the power of diminishing it in every degree; where¬ 
by at all times such portions, and only such portions of 
light are admitted, as may be received without injury to 
.he sense. 
There appears to be also in the figure, and in some prop¬ 
erties of the pupil of the eye, an appropriate relation to 
the wants of different animals. In horses, oxen, goats, 
sheep, the pupil of the eye is elliptical; the transverse 
axis being horizontal; by which structure, although the 
eye be placed on the side of the head, the anterior elon¬ 
gation of the pupil catches the forward rays, or those 
which come from objects immediately in front of the ani¬ 
mal’s face. 
CHAPTER XIII. 
PECULIAR ORGANIZATIONS. 
I believe that all the instances which I shall collect 
under this title, might, consistently enough with technical 
language, have been placed under the head of Comparative 
Anatomy. But there appears to me an impropriety in the 
use which that term hath obtained: it being, in some sort, 
absurd to call that a case of Comparative Anatomy, in 
which there is nothing to “compare;” in which a confor 
mation is found in one animal, which hath nothing proper- 
M* 
