EVOLUTION OF THE HUMAN FORM. 5° 7 



stages. Land life was therefore handicapped by its origin. It had to 

 start with what the ocean had to offer, and to begin with physical 

 conditions which afterward could, at the best, only be modified. 

 These conditions have left ineradicable traces even in man, the most 

 removed of all from the original types. Of water animals only the 

 elongated forms sent representatives to people the land — the worm, 

 mollusk, arthropod and vertebrate. And of these, the latter two alone 

 seemed well adapted to their new habitat, the arthropod developing 

 into an extraordinary multitude of species, though its inferiority of 

 organization removed it, at the start, from any competition with the 

 vertebrate as a basis for the higher evolution. We find in the bee 

 and the ant the ultimate development of the insect intellect, and the 

 insect form is decidedly restricted by its characteristic condition. 



Despite the immense variation that has taken place in land ver- 

 tebrates, their marked departures from the fish t3rpe have not been nu- 

 merous. One of the most important of these was the development of 

 the fin into the limb, yielding the quadruped. Another was the replace- 

 ment of the gill by the lung. But varieties of partially air-breathing 

 and four-paddled fishes still exist, as if to serve us as object lessons 

 in these stages of development. 



Land animals were exposed to much more varied natural conditions 

 than water animals and the struggle for existence between different 

 forms was quite as acute. Yet, though a vast number of differing 

 forms appeared, they were all built on the original lines of structure, 

 the type of organization of the fish strictly limiting that of the land 

 vertebrate. A development takes place, but it is on the lines already 

 laid down. The internal organs vary and become more effective in 

 action, the cold-blooded is succeeded by the warm-blooded, the egg- 

 bearing by the young-bearing, etc. There is much change in external 

 form. Animals became adapted to running, to flying, to swimming, 

 to crawling, to burrowing. There are many variations in the feet and 

 limbs, and in some cases these vanish, as in the serpent and the whale. 

 Some animals are clothed in scales or bony armor, some in hair or 

 feathers. But no new type appears, and though the mental powers 

 increase, ages pass with little indication of the coming of any animal 

 possessed of advanced powers of thought. Mentally the higher land 

 vertebrate progresses far beyond its highest water kindred, but its pow- 

 ers of thought, after gaining a certain development, remain in great 

 measure dormant, and there is nothing to indicate that the quadruped 

 could ever progress in thought beyond a certain low level. If so on 

 the earth, probably so everywhere : the influences acting on the quad- 

 ruped do not seem calculated to produce any advanced thinking powers. 



We have, in the foregoing pages, followed in its general features 

 the evolution of animal life upon the earth. In view of the immense 



