104 DEVELOPMENT AND HEREDITY. 



stable, impressionable constitution of living matter, 

 and to the effects of repetition known as retention 

 and association. An examination of the general 

 method of development shows that it is everywhere 

 the perfecting of a process by continued repetition 

 of the process. 



In nature we find that no individual organism 

 acquires any of its parts or organs suddenly and 

 in their full perfection. Each organ or part is the 

 result of slow growth, and develops gradually 

 from the imperfect to the more perfect state. 

 Moreover, in tracing the course of evolution, we 

 find the same law to be true of the appearance 

 of organs in the species or class. The organs do 

 not appear suddenly as new and perfect parts in 

 any one generation, but they are the product 

 of the long process of graded development through 

 many generations. The proper development of 

 each organ, and the function of the organ, are 

 inseparably linked and interdependent on each 

 other.' The function must have a controlling effect 

 on the development of the organ, and vice versa the 

 structure of the organ must limit the function. 

 It follows, therefore, that both in the individual 

 and in the race, the organ and its function have 

 been gradually perfected. Take, for example, the 

 function of an organ like a leg or wing, which 



