IO 



PHYSIOLOGY AND MORPHOLOGY OF ANIMALS. 



all. This is called (5) descriptive zoology. This consti- 

 tutes, along with taxonomy, systematic zoology. 



But the scope of the subject is not yet exhausted. 

 The earth has been inhabited for millions of years, and 

 the animal forms have been changing during all this time 

 according to certain definite laws. The study of extinct 

 forms, and especially the laws of succession of forms, 

 constitutes another department, called (6) palczozoology. 



Finally, the animals inhabiting different parts of the 

 earth are very different from one another. The causes 

 of these differences and their laws constitute another 

 absorbingly interesting department, for which no uni- 

 versally accepted name has yet been proposed. It has 

 been called chorology, but is usually spoken of as geo- 

 graphical distribution of animals, or (7) geographical zoology. 



Thus, then, the main departments of zoology are : 



1. Comparative anatomy or morphology. 



2. Comparative physiology. 



3. Comparative embryology. 



4. Taxonomy, or classification ) 



^ ■" L systematic. 



5. Descriptive zoology j 



6. Palaeozoology. 



7. Geographical zoology. 



Each one of these departments, constitutes a field of 

 study sufficient to occupy the lifetime of any one. It 

 is evident, then, that we can not take up all these with 

 equal fullness. Instruction spread over so wide a field 

 must be far too meager. We select, then, as our cen- 

 tral subject the second one, comparative physiology of ani- 

 mals. For this, which deals with the phenomena of ani- 

 mal life, is certainly the department to which all others 

 are tributary. But it is impossible to understand function 

 without a knowledge of structure, with which it is as- 

 sociated. Therefore our subject will be physiology, and 

 so much anatomy or morphology as is necessary to ex- 



