EVOLUTION THE RESULT OF CHEMICAL FORCES. 103 



The earth had passed more than half of its life-bearing age 

 before a single air-breathing animal had appeared. Up to about 

 the period of the Carboniferous formation all animals had lived 

 in the water, the highest forms being fishes of the shark type, 

 undoubtedly the air at that time was loaded with carbonic oxide, 

 and the profuse vegetation of those eras was needed to clear the 

 atmosphere of noxious gases and render it fit for respiration. 

 But about the time we have mentioned the record of the rocks 

 shows the appearance of an amphibious animal, the labyrintho- 

 dont, with gills to breathe in the water and lungs to breathe in 

 the air. It had feet with five toes, the double bones of the 

 lower leg, the shoulder and collar bones, in short all the essential 

 parts which make up the perfect mammalian frame-work. It 

 was as different in its skeletal structure from any fish that then 

 lived, as a beast is different from a fish to-day. The skeleton 

 of the first amphibian was an immense advance on anything that 

 had gone before it. It was the model on which, without the 

 addition of a structural bone, has been constructed the varied 

 frame-work of all air-breathing vertebrate animals. 



There is no instance in the development of vertebrates above 

 the fishes, where any structural bones have been formed anew or 

 added to the frame. If there were any modifications to be made, 

 they were simply changes in form and function, or more often 

 the entire elimination of certain bones or members. The zebra, 

 horse and ass, as we have seen, in the course of ages, by dropping 

 successively the phalangial members, have finally come to possess 

 only one, the middle toe. The ox and camel have got rid of all 

 but two. The normal and original number however is always 

 five ; and man, as well as anthropoid apes, still retain the full 

 complement. Therefore every species that has ever been in the 

 line of man's derivation, back to the primeval batrachian, must 

 have had the full complement of structural bones, the five fingers 

 or toes, the double bones of the fore-arm or leg, the scapula and 

 clavicle, and so on. But no fish that ever swam has any of these 

 parts in any wise resembling those of air-breathing animals. For 

 this reason I say that the production of the first lowly amphibian 

 that crawled out of the water to live on land, was a miracle in 



