ANIMAL MECHANICS. 



423 



that they were very like each other — simply because he would 

 consider only their superficial resemblances, and would be 

 unable to appreciate the purposes which the machines were 

 respectively intended to fulfil. In like manner, anatomists, 

 from observation of apparent resemblances in the structure of 

 organs, such as the brain (of the specific action of whose parts 

 little or nothing is known), have sometimes, rashly, inferred a 

 greater degree of affinity between various animals than there 

 is any logical ground for admitting. If we confine our atten- 

 tion to the arrangement of muscles and bones, the objects and 

 uses of which are perfectly known and understood, we may 

 readily perceive that, under a superficial appearance of simi- 

 larity of parts, there really exists a profound difference of 

 function and intention as to the purposes to which these 

 organs are devoted. In the present state of anatomical 

 science, it seems safer to collect facts and physical constants, 

 characteristic of each group of organs in various animals, than 

 to indulge in premature speculations as to possible modes of 

 production of such organs. In the language of the schoolmen, 

 the Final Cause of the wing of a bird is to fly in air, and the 

 Final Cause of the fore-limb of an Otter or Seal is to swim in 

 water ; and we can show that the intention of the organ is, in 

 each case, perfectly fulfilled ; but it appears unscientific to 

 speculate as to the possible derivation of one of these struc- 

 tures from the other, by means of an hypothetical common 

 ancestor. 



I shall now give the muscular type of the wings of two 

 large Bats, Pteropus edulis and Epomophorus Whitii, for the 

 purpose of comparing it with the type of the wings of 

 birds : — 



