i66 Darwin, and after Darwin. 



the enormous profusion of the extinct species on the 

 one hand, and to the immense number of known 

 fossils on the other, it was incredible that no satis- 

 factory instances of specific transmutation should ever 

 have been brought to light, if such transmutation had 

 ever occurred in the universal manner which the theory 

 was bound to suppose. But since Darwin first 

 published his great work palaeontologists have been 

 very active in discovering and exploring fossiliferous 

 beds in sundry parts of the world ; and the result of 

 their labours has been to supply so many of the 

 previously missing links that the voice of competent 

 criticism in this matter has now been well-nigh silenced. 

 Indeed, the material thus furnished to an advocate of 

 evolution at the present time is so abundant that his 

 principal difficulty is to select his samples. I think, 

 however, that the most satisfactory result will be 

 gained if I restrict my exposition to a minute account 

 of some few series of connecting links, rather than if 

 I were to take a more general survey of a larger 

 number. I will, therefore, confine the survey to the 

 animal kingdom, and there mention only some of the 

 cases which have yielded well-detailed proof of con- 

 tinuous differentiation. 



It is obvious that the parts of animals most likely 

 to have been preserved in such a continuous series of 

 fossils as the present line of evidence requires, would 

 have been the hard parts. These are horns, bones, 

 teeth, and shells. Therefore I will consider each of 

 these four classes of structures separately. 



Horns wherever they occur, are found to be of high 

 importance for purposes of classification. They are 



