DARWIN'S EVIDENCES 13 



plete parallelism between the development of the individual 

 and the history of the race, nor should we expect to do so, 

 since embryonic as well as adult stages may be modified in the 

 course of evolution; what we should expect is a more or less 

 vague historical sketch, and this is what is usually found 

 remaining. 



"3. Morphology. On comparing together the different 

 members of one of the great groups or classes of animals or 

 plants, we find the same fundamental plan of organization 

 running through all of them. Series of corresponding organs 

 are often to be made out which are built upon the same 

 general scheme, although their functions may be quite dis- 

 similar; so that, for instance, in the hand of a man, the paw 

 of a dog, the wing of a bat, and the paddle of a whale, almost 

 identically the same series of bones can be traced. An ob- 

 vious explanation is to be found in the supposition that these 

 parts have arisen by the divergent modification of parts 

 which were originally identical. 



"4. Geographical Distribution. Observation shows that 

 groups of closely allied creatures are often found living in 

 neighbouring districts, and that when such a barrier as an 

 ocean or a range of lofty mountains is passed an entirely new 

 fauna and fiora are usually to be met with. These facts may 

 be explained by the hypothesis that allied groups of species 

 originated by a process of descent in the same countries which 

 they now inhabit, and they can be explained by no other 

 known hypothesis. 



" 5. The Geological Succession of Organisms. The general 

 facts regarding the distribution of allied species of animals 

 and plants in time point in precisely the same direction as 

 those relating to their distribution in space. In a few cases, 

 notably in that of the extinct horse of North America, a long 

 chain of possibly ancestral types has been found leading back 

 to a remote and very different progenitor. This supposed 

 ancestor of the horse was a creature little larger than a 

 moderate-sized dog. It had four separate toes to each fore- 

 limb, and three to each hind-limb, and its teeth were much 



