GREAT STEPS IN EVOLUTION 97 



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, tJherjg is the wealth of con- 

 gimmiia.tg a.d apt? t.ion 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 adaptation^ 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. Jlag skes 



were the first 



fl.m'rrmls with skulls: fishes were 



fr II f I Mllf| 1- , | || > ^ !! *TT il ifcl 



j^aws ; gj^phjbians jgaiflQ^ ..fiBS?r s Lftfl^r^ ^^ 



true lungs* a voice, and a 



*" . '. 



iTs^ the important antenatal 

 robes (oi^foetaljnembranes) called the amnion 

 and the allantois, ancTtiie crocodile wfts the 

 first creature^with a four-chambered heart ; 



