4 GENERAL PRINCIPLES OF ZOOLOGY 



one generation to another in other words, the laws of heredity has 

 recently made a great advance by investigations in two directions: (i) 

 through the biometric method or the statistics of variation, and (2) by 

 the so-called 'Mendelian analysis' of the hereditary potentialities. Both 

 lines of investigation (to be considered more in detail later) have opened 

 up in an unexpected way the possibility of submitting to exact research 

 the questions of variation and heredity, fundamentally important for the 

 understanding of the living world. 



Biology. According as the relations of each organism to the external 

 world are brought about through its vital phenomena, there belongs to 

 physiology, or at least is connected with it, the study of the conditions of 

 animal existence, (Ecology, often called Biology in the narrower sense, 

 the broader meaning being the science of all living things, both animals 

 and plants. This branch has of late attained considerable importance. 

 How animals- are distributed over the globe, how climate and condi- 

 tions influence their distribution, how by known factors the structure 

 and the mode of life become changed, are questions which are to-day 

 discussed more than ever before. 



Paleontology. Finally to the realm of zoology belongs also Paleozo- 

 ology or Paleontology, the study of the extinct animals. For between the 

 extinct and the living animals there exists a genetic connection: the former 

 are the precursors of the latter, and their fossil remains are the most trust- 

 worthy records of the history of the race, or Phylogeny. 



