GEOGRAPHICAL DISTRIBUTION. 12$ 



from the germ to the adult, is a very different thing from the 

 history of the steps by which the same individual acquired 

 the differences which distinguish it from other species of the 

 same genus, which is the particular meaning of evolution. 

 Evolution is the process of modification of specific characters, 

 and development is the process of forinatio}i of individual 

 characters. There are also conditions incident to these proc- 

 esses — conditions which are both outside of and exist before 

 each step of these processes. When these conditions are 

 essential!}' connected with the preparatory organic functions 

 by which the processes are carried on, they are intrinsic, and 

 they are defined under the general term ancestry ; when they 

 are accidental to the time or place when and where the pro- 

 cesses are acting, they are extrinsic, and are called the condi- 

 tions of environment. 



Immutability or Mutability of Species. — The fundamental 

 difference between the old and new schools of naturalists is 

 found in their opinions regarding the origin of specific differ- 

 ences : the old school held the doctrine of the ininiutability of 

 species, the new holds the doctrine of the mutability of species. 

 The result of the change of view has not invalidated the 

 observations of the earlier naturalists, but it has produced a 

 complete revolution in the methods of interpretation of 

 natural history. 



In this conception, defined by Forbes, we see that among 

 the contributions which ancestry brings to the actually known 

 individual there are what he called the ''specific characters" 

 which distinguish it from every other species, and the posses- 

 sion of these "specific characters " was taken to support the 

 notion of derivation from the original protoplast. 



Descent was recognized as without modification ; that is, 

 the law of descent was the perpetuation of the ancestral 

 "specific characters" in the offspring. There was in the 

 definition no consideration of the origin of such specific char- 

 acters. Whatever modifications occurred in the offspring 

 were defined as irregularities of growth, whose cause was 

 located in the idiosyncrasies of the individual, or in what is 

 above called environment, but they were not supposed to be 

 perpetuated. 



