4 ANIMAL BIOLOGY 



characteristics of protoplasm. So much for the study of the adult 

 individual animal or plant — but this is not all. The origin and 

 development of the individual, genetics and embryology; and 

 the origin and development of species, organic evolution, are 

 other wide fields which must be approached from both the struc- 



Fig. 1. — The chief divisions of Biology. 



tural and functional aspect if any real advance is to be made to- 

 ward a comprehensive appreciation of life. (Fig. 1.) * 



Thus, just as the various physical sciences have expanded and 

 become specialized until they are beyond the grasp of a single man, 

 so biology and its subdivisions, or the biological sciences, are 

 now distributed among many specialists. Although specializa- 

 tion results in a narrowing and isolating of the fields of study, as 

 deeper levels of investigation have been reached in all the sciences 

 there has been a tendency for the basic phenomena to meet on the 

 common ground of the fundamental sciences, physics and chem- 

 istry — for in the last analysis the biologist must assume, as a 

 working hypothesis, that the properties of protoplasm are the re- 



1 In order not to interrupt the continuity of the narrative, formal definitions of 

 technical terms are usually omitted from the text. See the glossary, Appendix III. 



