,10 
OF THE ANlMAt STRUCTURE 
imal bodies much to be admired. Of ten thousand eyes, I 
do not know that it would be possible to match one, except 
with its own fellow; or to distribute them into suitable pairs 
by any other selection than that which obtains. 
This regularity of the animal structure is rendered more 
remarkable by the three following considerations:—First, 
the limbs, separately taken, have not this correlation of 
parts; but the contrary of it. A knife drawn down the 
chine, cuts the human body into two parts, externally equal 
and alike; you cannot draw a straight line which will di¬ 
vide a hand, a foot, the leg, the thigh, the cheek, the eye, 
the ear, into two parts equal and alike. Those parts which 
are placed upon the middle or partition line of the body, or 
which traverse that line, as the nose, the tongue, the lips, 
may be so divided, or, more properly speaking, are double 
organs; but other parts cannot. This shows that the cor¬ 
respondency which we have been describing, does not 
arise by any necessity in the nature of the subject: for, if 
necessary, it would be universal; whereas it is observed only 
in the system or assemblage: it is not true of the separate 
parts; that is to say, it is found where it conduces to beau¬ 
ty or utility; it is not found where it would subsist at the 
expense of both. The two wings of a bird always corres¬ 
pond: the two sides of a feather frequently do not. In cen¬ 
tipedes, millepedes, and that whole tribe of insects, no two 
legs on the same side are alike; yet there is the most exact 
parity between the legs opposite to one another. 
2. The next circumstance to be remarked is, that whilst 
the cavities of the body are so configurated, as externally 
to exhibit the most exact correspondency of the opposite 
sides, the contents of these cavities have no such corres¬ 
pondency. A line drawn down the middle of the breast, 
divides the thorax into two sides exactly similar; yet these 
two sides enclose very different contents. The heart lies 
on the left side; a lobe of the lungs on the right; balancing 
each other neither in size nor shape. The same thing 
holds of the abdomen. The liver lies on the right side,* 
without any similar viscus opposed to it on the left. The 
spleen indeed is situated over against the liver; but agree¬ 
ing with the liver neither in bulk nor form. There is no 
equipollency between these. The stomach is a vessel, both 
irregular in its shape, and oblique in its position. The fold-* 
ings and doublings of the intestines do not present a parity 
* The principal lobe of the liver is on the right, hut a smaller is extend-* 
ed into the left aide. See Plate XXII. 
