244 NATURAL THEOLOGY. 



spective tribes, the instruments of their motion; 

 but, in the work which they have to do, there is a 

 considerable difference, founded in this circum- 

 stance. Fish, unlike birds, have very nearly 

 the same specific gravity with the element in 

 which they move. In the case of fish, therefore, 

 there is little or no w'eight to bear up ; \\\mt is 

 w^anted, is only an impulse sufficient to carry the 

 body through a resisting medium, or to maintain 

 the posture, or to support or restore the balance 

 of the body, which is always the most unsteady 

 w^here there is no w^eight to sink it. For these 

 offices, the fins are as large as necessary, though 

 much smaller than wings, their action mechanical, 

 their position, and the muscles by w^hich they are 

 moved, in the highest degree convenient. The 

 following short account of some experiments upon 

 fish, made for the purpose of ascertaining the use 

 of their fins, will be the best confirmation of w^hat 

 we assert. In most fish, besides the great fin, the 

 tail, w^e find two pairs of fins upon the sides, two 

 single fins upon the back, and one upon the belly, 

 or rather between the belly and the tail. The 

 balancing use of these organs is proved in this 

 manner. Of the large-headed fish, if you cut off 

 the pectoral fins — /. e., the pair which lies close 

 behind the gills — the head falls prone to the 

 bottom : if the right pectoral fin only be cut off, 



vary, but yet they are accommodated in a manner so perfect, that, 

 on examining any individual among the varieties of the species, 

 we should say that nothing could be better suited to its purpose. 



