economy, even though this may be a relatively passive one; 

 while on the other hand we do not know in science at any 

 rate of a function that is devoid of a material basis. The 

 division is made solely for the sake of analysis, and it de- 

 pends entirely upon the point of view. Morphology treats 

 adult animals, their different developmental stages, and, 

 / more naturally, the remains of extinct animals as though 

 they were arrested in their living, but the dynamic aspects 

 of organic life are so prominent and insistent that it is 

 really impossible to ignore them even temporarily. 



Besides dealing with the same materials, the many com- 

 plicated problems of zoology are still further connected in 

 that the central object of study for both the structural and 

 physiological divisions is evolution. As we look back over 

 the history of the subject from our modern vantage- 

 ground, we can see how zoology began with ancient and 

 mediaeval natural history, how from this parent stock arose 

 the additional separate branches of anatomy, embryology, 

 paleontology and distribution, how human physiology be- 

 came comparative physiology which developed later into 

 the broad and deep enquiry into all the activities of ani- 

 mals, their vital relations to one another, and their reac- 

 tions to and upon the environment; and we can see how 

 all these several branches were vitalized by the great prin- 

 ciple of evolution. This whole history shows a steady 

 progress through one phase after another toward the mod- 

 ern study of evolution, though the naturalists of the 

 eighteenth and even of much of the nineteenth century 

 were unconscious, in whole or in part, of the way their ob- 

 servations and views were contributing to the establish- 

 ment of the doctrine of descent and to the partial descrip- 

 tion that can now be offered of the natural factors of 

 evolution. As we shall see, the structural analysis of ani- 

 mals demonstrates the evolution of species as a universal 

 process, while the broad study of the dynamic relations of 



7 



