MAIN PATHWAYS AND TENDENCIES in 



operations depend responses to stimuli, fermenta- 

 tion and digestion, circulation, secretion, excretion, 

 reproduction of animals, etc. But physiology is also 

 an independent science, pursued for its own sake, and 

 statements like those just made are not to be taken 

 even to imply that physiology in this sense is a part 

 of zoology. A parallel situation exists in reference to 

 anatomy, which is a separate science, whilst the 

 comparative anatomy of animals is a major subject 

 of zoology. Physiology, is broadly biological, and 

 this constant overlapping of closely related subjects is 

 to be expected. 



The study of the reactions of the protozoa to va- 

 rious stimuli has been much cultivated both in 

 zoology and in physiology since these organisms 

 exhibit life in relatively simple expressions. The 

 illuminating quality of such experimental studies has 

 been so fully recognized, that modern text-books on 

 human physiology, in most cases, begin with an 

 analysis of the properties of protoplasm and the 

 physiological reactions of the protozoa. This is the 

 best means of introduction to the study of experi- 

 mental physiology. 



Animal Psychology and Animal Behavior. The 

 divisions of animal psychology and animal behavior 



