452 LECTURE XVI. 



carried on slowly, but wL.iclij in their totality, exceed anything 

 we are able to observe within the span of time open to our 

 view. The upheavings and subsidences of continents, the 

 altered proportions of land to sea, the gradations of climates, 

 in short, all changes on the surface of the earth made known 

 to us by geology, have not been effected by sudden convulsions, 

 but have been gradually and impercepibly produced. The 

 changes in the animal world have proceeded pari passu, and 

 while many inflexible races have perished, others have been 

 transformed, and thus present a series of changes, the terminal 

 points of which deviate so much, that families, orders, classes, 

 might have issued from them. 



It has long been acknowledged that the actual creation re- 

 presents by no means an ideal whole, the members of which 

 are harmoniously connected, and that it can only be considered 

 in its ensemble by including the extinct animals. What in the 

 present animal world appears as perfectly distinct becomes 

 cemented by the transitions represented in extinct animals, 

 so that every new discovery adds an intermediate link in the 

 series of forms. Just as in the external animal world, no 

 definite boundary-line can be drawn between fishes and am- 

 phibia, inasmuch as the genera Lepidosiren and Protopterus 

 present the most evident transitional forms, so that, according 

 as a naturalist considers this or that character the more essen- 

 tial, they are by one author included in fishes, by another in 

 amphibia, so it is with a multitude of transitional forms found 

 among organic remains. The boundary-line between amphibia 

 and reptiles, which may be drawn in the present creation, no 

 longer exists when we look at the singular family of Laby- 

 rinthodonts, which extends to both. The boundaries be- 

 tween herbivorous Cetacea and Pachydermata, between these 

 latter and ruminants, are removed by the Dinotherium and the 

 Dicliohune. The feathered reptile* of Solenhofen indicates that 

 nature is able to bridge over the gulf between reptiles and 

 birds. The existence of these transition forms is undeniable 

 — their significance does not consist merely in the filling up of 



* Proved satisfactorily to have been a bird with a long series of caudal 

 vertebrae. — Editor. 



