6 THE MAIN CURRENTS OF ZOOLOGY 



such an account untechnical and not in too great 

 detail. There are excellent text-books, in which the 

 animal kingdom is systematically considered, but 

 there is need of a source of collateral reading to 

 supplement these text-books and to run parallel with 

 laboratory work and field observations. 



Position of Zoology in Biology. To fix the 

 place of zoology we need only to remember that one 

 of the most striking developments of the past half- 

 century has been the great extension of knowledge of 

 organic nature and the new interpretations that have 

 resulted. Since zoology is the central subject of 

 this biological advance, it has come about that this 

 science embodies our interpretations of organic 

 nature. There comes within its province considera- 

 tion of all the phenomena of animal life and of what 

 has grown out of their study: Evolution, genetics, 

 heredity, biogenesis, Mendelism, transmission of 

 disease through animal agencies, structure, devel- 

 opment, habits, animal intelligence and behavior. 

 These and kindred matters find in zoology their 

 illustrations and their systematic treatment. 



Inasmuch as most animals possess a nervous sys- 

 tem, which is lacking in plants, zoology gives a fuller 

 representation of vital phenomena than its sister 



