Superfluous Structures 97 



all the activities. The structure of an animal is therefore 

 adjusted to its particular mode of life in all of its parts. A 

 bird of prey, for example, differs from a seed-eating ground 

 bird in every detail of structure. Not only the claws and 

 the beak, but the eye and the viscera, the skeleton and the 

 muscles are characteristic for its mode of life. It was on 

 this doctrine of correlation that Cuvier thought he could 

 recognize an animal from almost any sample taken from 

 its body. And indeed he did do remarkably well in recon- 

 structing fossil animals from mere fragments, for there is a 

 kernel of sound truth in this principle, although most com- 

 parative anatomists since Cuvier's time do not attach to it 

 as much weight as he did. 



There is, however, another sense in which all life is 

 one. That is the fact that we are unable to locate " life " in 

 any particular part of the plant or animal body, but find 

 that being alive is a condition of the organism as a whole. 

 It is true that portions of an animal can be removed without 

 killing the individual, and that portions themselves may be 

 maintained as growing pieces of tissue. Dr. Alexis Carrel 

 of the Rockefeller Institute has maintained fragments of 

 chicken tissue ** alive " for over fifteen years. It is the whole 

 organism, however, that can maintain itself and reproduce 

 itself, and the parts have meaning only in relation to the 

 organism as a unity. 



Recognizing then that all living things have so much 

 in common and that the organism characteristically main- 

 tains itself as a unity toward the outside world, it becomes 

 difficult to reconcile observed facts with the idea that each 

 species was especially created for the place in the world in 

 which we find it, and that its various parts and activities 

 were supplied it from the first to suit its needs. 



Superfluous Structures 



When we compared the different classes of vertebrate 

 animals emphasis was placed on the unity of structure run- 



