THE ENERGY OF LIFE EVOLUTION. 



79 1 



physical impress of the environment, as temperature, light, humidity, 

 movements of the medium, etc., which are only influenced by the ani- 

 mal as it places itself, by its movements, within or without the 

 range of their influence. In spite of these facts, I believe the move- 

 ments and habits of animals to lie at the foundation of their principal 

 characters, and that the superstructure, be it due to whatever cause 

 it may, rests upon that foundation. It will now be well to take a 

 look at the evidence in favor of or against these theories, as pre- 

 sented by the science of vertebrate paleontology. A few examples 

 will suffice. 



In the first place, I will select an illustration of the effects of use 

 on the articulations of the limbs and feet of the mammalia. I take 

 first the ankle- and wrist-joints. In the ruminating animals (ox, deer, 

 camel, etc.) and in the horse, among other living species, the ankle- 

 joint is a very strong one, and yet admits of an extensive bending of 

 the foot on the leg. It is a treble tongue-and-groove-joint ; that is, 

 two keels of the first bone of the foot, the astragalus, fit into two 

 grooves of the lower bone of the leg, the tibia, while between these 

 grooves a keel of the tibia descends to fill a corresponding groove of 

 the astragalus. Such a joint as this can be broken by force, but it 

 cannot be dislocated. Now, in aH bones the external walls are com- 

 posed of dense material, while the centers are spongy and compara- 

 tively soft. The first bone of 

 the foot (astragalus) is narrower, 

 from side to side, than the tibia 

 which rests upon it. Hence the 

 edges of the dense side-walls of 

 the astragalus fall within the 

 edges of the dense side-walls of 

 the tibia, and they appear to have 

 pressed into the more yielding 

 material that forms the end of 

 the bone, and pushed it upward, 

 thus allowing the side-walls of 

 the tibia to embrace the side- ; - 

 walls of the astragalus. Now, }- 

 this is exactly what would hap- '- 

 pen if two pieces of similar dead 

 material, similarly placed, should 

 be subjected to a continual 

 pounding in the direction of Fig. i Hind-foot of Coryphodon elephanto- 



,.,.,, . . , pus, 6howing flat astragalus for ankle-joint. 



their length tor a long period (From Eocene bed of New Mexico.) One half 



j. , a j j. natural size. 



of time. And we can not as- 

 cribe any other immediate origin to it in the living material ; but the 

 probability of such origin is more probable in such substance, because 

 of the perpetual waste and repair which are going on, and because of 



