204 DEVELOPMENT AND HEREDITY. 



to the same unchanging environment. Darwin 

 speaks of the changes of growth, in a species re- 

 sulting from a general change in environment, as 

 the "breaking of the constitution of the species." 

 After the constitution is broken, the species pro- 

 duces many variations of growth. It is to be sup- 

 posed that, if the new conditions were to endure for 

 a great length of time, the constitution of the spe- 

 cies, with its newly induced characters, would again 

 become "fixed." Our domesticated plants and ani- 

 mals are species which, being subjected to a change 

 of conditions from their wild state, have had their 

 "constitutions broken," and ever since, being sub- 

 jected to constantly changing conditions of locality, 

 soil, climate, cultivation, and breeding, have contin- 

 ued in a highly variable state. 



Any change in the stimuli acting upon a species, 

 in order to produce a change in the hereditary im- 

 pulse, must continue its action long enough to affect 

 the nervous co-ordinations. As a rule, the hereditary 

 impulse is not affected by a change which acts on 

 only one generation. The so-called "individually 

 acquired characters," which are produced by the 

 temporary action of peculiar forces upon a single 

 individual, are not inherited, because the nervous co- 

 ordinations are not so greatly disturbed that they can- 

 not, in the next generation, under the normal stimuli 

 of the species, react in the normal method of devel- 



