GREAT STEPS IN EVOLUTION 97 



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' dactyls mark the mastery of the air in which 

 Birds and Bats are now most at home. But 

 hardly less impressive is the possessing of 

 every nook and corner. Many a species has 

 only a niche, but it is its own. (6) Following 

 from the masterful, detailed colonization of 

 the heavens and the earth and the waters 

 under the earth, there is the wealth of con- 

 summate adaptation — of a creature to its 

 surroundings, to its food, to its habits; of the 

 unborn young to the mother and of the 

 mother to the unborn young; of the sexes to 

 one another; and of the internal architecture 

 of the body, whether in the fit adjustment of 

 the proportions of parts, or in the minute 

 structure of a bone. Every creature is a 

 bundle of adaptations. Indeed, as Weis- 

 mann says of the whale, "When we take 

 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; amphibians gained fingers and toes, 

 true lungs, a voice, and a mobile tongue; 

 reptiles first show the important antenatal 

 robes (or foetal membranes) called the amnion 

 and the allantois, and the crocodile was the 

 first creature with a four-chambered heart; 



