GREAT STEPS IN EVOLUTION 09 



away the adaptations, what have we 

 left ? " 



It is instructive to look into the matter in 

 detail, and to notice, for instance, what types 

 made particular acquisitions. Hag fishes and 

 lampreys (Cyclostomes) were the first animals 

 with skulls; fishes were first with jaws; amphi- 

 bians gained fingers and toes, true lungs, a 

 voice, and a mobile tongue; reptiles first show 

 the important antenatal robes (or foetal mem- 

 branes) called the amnion and the allantois, 

 and the crocodile was the first creature with 

 a four-chambered heart; birds and mammali 

 are the only warm-blooded animals, and they 

 show a great heightening of brain-develop- 

 ment; in all mammals except a few primitive 

 forms there is an extremely important and 

 usually prolonged intimate connection be- 

 tween the mother and the unborn young. 



THE ASCENT OF MAN. As this final achieve- 

 ment of Vertebrate evolution will be discussed 

 by Dr. Arthur Keith in a special volume of 

 this Library, we need not do more than refer 

 to a few points of general evolutionary 

 interest. 



The real distinctiveness of man from his 

 nearest^ allies depends on his power of building 

 up general ideas and of controlling his~conduct 

 in relation to ideals. He has many structural 



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