128 NATURAL THEOLOaY. 



more be done iii order to make the curve truj, that is, the 

 parts equidistant from the middle, ahke in figure and po- 

 sition ? 



The exact resemblance of the eyes, considering hoAV com- 

 pounded this organ is in its structure, how various and how 

 delicate are the shades of color with which its iris is tinged ; 

 liow differently, as to effect upon appearance, the eye may 

 be mounted in its socket, and how differently in different 

 heads eyes actually are set — is a property of animal 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 othei 

 selection than that which obtains. 



This regularity of the animal structure is rendered more 

 remarkable by the three following considerations : 



1 . The limbs, separately taken, have not this correlation 

 of parts, but the contrary of it. A knife drawn do^\ii the 

 chine cuts the human body into two parts, externally equal 

 and alike ; you cannot draw a straight line which will divide 

 a hand, a foot, the leg, the thigh, the cheek, the eye, the ear, 

 mto two parts equal and ahke. Those parts which are 

 placed upon the middle or partition line of the body, or 

 which traverse that line — as the nose, the tongue, and the 

 lips — may be so divided, or more properly speaking, are 

 double organs ; but other parts cannot. This shows that 

 the correspondency w^hich 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 sep- 

 arate parts : that is to say, it is found where it conduces to 

 beauty or utility ; it is not found where it would subsist at 

 the expense of both. The two wings of a bird always cor- 

 respond ; the two sides of a feather frequently do not. In 

 centipedes, millepedes, and the 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. 



