4 GENERAL TRINCirLES OF ZOOLOGY 



one generation to anotlier — in ot]ier worils, the laws of heredit)' — has 

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

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

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

 lines of investigation (to lie considered more in tleiail later) ha\'e opened 

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

 the questions of variation and heredity, fundamentally important for the 

 understanding of the li\"ing world. 



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

 world are brought about through its ^ital phenomena, there belongs to 

 physiology, or at least is connected with it, the stud)" of the conditions of 

 animal existence, CEcology, often called Biology in the narrower sense, 

 the broader meaning being the science of all liA-ing 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 I'aleozo- 

 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 liistory of the race, or Phylogenv. 



