216 SPECIES NOT 



the variation of some species. But to bring it 

 forward to illustrate the origin of a fish, a rep- 

 tile, a bird, and a ,mammal, from one parent 

 form, is not sound. It must not be forgotten 

 that vertebrate animals of different classes do not 

 merely differ from each other in fins, and wings, 

 and hands, or in living in diverse elements, 

 and breathing, digesting, and circulating their 

 blood in various modes, and by apparatuses very 

 different, but that they are clearly distinct organ- 

 isms, formed with reference to the individual. A 

 bird, for instance, is not made up of the different 

 parts in a fish, put together so as to constitute 

 a bird, nor is a mammal an aggregate of the 

 constituent organs of a bird; but each mammal, 

 bird, reptile, and fish, has its most minute parts 

 formed in reference to the individual, and its 

 mode of life. Each being is perfect in itself, 

 and it would be as impossible, physiologically 

 speaking, to convert a fish into a bird, a bird 

 into a mammal, or to degrade a bear into a 

 whale, as it would be to transmute ideally a man 

 into an oak tree. Not only the form of the 

 skeleton, but the histological anatomy of the 

 bone, is different; not only are the muscles dif- 

 ferently formed, and shaped, and attached, but 

 their minute anatomy is dissimilar. The brain 

 and nervous system differ widely in each, and 

 there are no two classes of vertebrate that 

 have the same sized blood discs, or capillary 

 vessels which convey them! How then can the 

 writer in the "Cornhill," a magazine, I presume, 



