INTRODUCTION 1 7 



tions. 1 The result is an important one from the 

 point of view of method. 



In biology, excepting in the case of individual 

 adaptation of artificial selection, direct observation 

 the historical method, if we may so call it is 

 not available for the study of the origin and 

 modification of organisms. Phylogeny, the science 

 of organic kinship, .resorts to other methods, and 

 particularly to the comparative method in its 

 various forms : 



(a) Morphology, the science of determining the 

 phylogeny of organs by comparing them with the 

 organs of other creatures belonging to the same 

 systematic group. 



(6) Palaeontology, which determines the direct 

 ancestors of living creatures. 



(c) Embryology, which, so far as it is founded 

 upon the principle of recapitulation, investigates 

 the development of organs in the individual, and 

 draws conclusions therefrom bearing upon its 

 descent. 



1 Among animals there is a special factor which gives a.stability 

 to the specific characters not found elsewhere this is reproduction. 

 Specific characters being common to the whole line of descent, are 

 very deeply enrooted in the organism. They are not easily modi- 

 fied by the influence of new environments, but maintain their 

 likeness to one another in spite of external conditions. They are 

 regulated by an internal force, notwithstanding the importunities 

 to variation offered from outside. This force is heredity, and 

 heredity accounts for the precise way in which specific characters 

 may be defined. In society this internal force is wanting. (Les 

 Regies de la metJwde sociologique. Durckheim, Paris, F. Alcan , 1895.) 



B 



