4 THE MAIN CURRENTS OF ZOOLOGY 



what must be included in the exposition of zoology 

 and what may be omitted becomes a perplexing one. 



Accordingly, at the outset, it is of primary im- 

 portance to get an idea of what is embraced within 

 the zoological territory and to determine the method 

 of analysis so as to give, if possible, a unified view of 

 this many-sided science. Undoubtedly, the be- 

 wildering number of details makes it difficult to deal 

 with them clearly and coherently. The attempt to 

 unite them into an orderly whole runs the risk of 

 becoming merely discursive. The matter, however, is 

 greatly simplified by the circumstance that in the 

 progress of zoology, notwithstanding the continual 

 multiplication of details, there has been continuity of 

 development of zoological thought. If we can follow 

 the path, the large number of details serves to enrich 

 the subject with numerous illustrations without con- 

 fusing it. 



The first step of our program should be to deter- 

 mine the main currents of zoological progress and, 

 thereafter, to become acquainted with the circum- 

 stances under which they were started and their 

 ultimate outcome. 



The direct study of animal types will not suffice. 

 Laboratory exercises and observation of animals in 



