442 POPULAR SCIENCE MONTHLY 



courses. I shall pass directly to a description of the elements of the 

 present science of zoology and of its history, so far as this is necessary 

 for a clear understanding of the various divisions of the subject and 

 of their connections ; and finally I shall endeavor to show how through 

 its human materials zoology articulates directly with other fields of 

 knowledge. 



Zoology is the science that deals with the structure, development 

 and inter-relationships of animals, with the workings of their parts, 

 their activities and their relations to their environment, and with the 

 factors that determine their forms. We may recognize two great divis- 

 ions of the subject, which are concerned respectively with static and 

 with dynamic principles, though the materials of both divisions are the 

 same — namely, all animals throughout the entire range from the high- 

 est to the lowest. It is of course clear that morphology — the science 

 of structure — can not be absolutely separated from physiology — the 

 science of function in its widest sense — for we do not know of organic 

 structures that play absolutely no part in an animal's 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 depends entirely upon the point of view. Morphology treats 

 adult animals, their different developmental stages, and, more natur- 

 ally, 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 complicated 

 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 medieval natural history, how from this parent stock arose the 

 additional separate branches of anatomy, embryology, paleontology and 

 distribution, how human physiology became comparative physiology 

 which developed later into the broad and deep enquiry into all the 

 activities of animals, their vital relations to one another, and their 

 reactions to and upon the environment; and we can see how all these 

 several branches were vitalized by the great principle of evolution. 

 This whole history shows a steady progress through one phase after 

 another toward the modern 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 observations and 

 views were contributing to the establishment of the doctrine of descent 

 and to the partial description that can now be offered of the natural 

 factors of evolution. As we shall see, the structural analysis of animals 



