190 THE INDUCTIONS OF BIOLOGY. 



capacity produced, to a very considerable degree, even after a 

 long period of desistance ; but one who lias persevered in such, 

 habits for but a short time, has, at the end of a like period, 

 scarcely any of the facility he had gained. Here, 



too, as before, successions of organisms present an analogous 

 fact. A species in which, domestication, continued through, 

 many generations, has organized certain peculiarities ; and 

 which afterwards, escaping domestic discipline, returns to 

 something like its original habits ; soon loses, in great mea- 

 sure, such peculiarities. Though it is not true, as alleged, 

 that it resumes completely the structure it had before domes- 

 tication ; yet it approximates to that structure. The Dingo, 

 or wild dog of Australia, is one of the instances given 

 of this ; and the wild horse of South America is another. 

 Mankind, too, supplies us with instances. In the Austra- 

 lian bush, and in the backwoods of America, the Anglo- 

 Saxon race, in which civilization has developed the higher 

 feelings to a considerable degree, rapidly lapses into compara- 

 tive barbarism : adopting the moral code, and sometimes the 

 habits, of savages. 



§ 68. It is important to reach, if possible, some rationale 

 of these general truths — especially of the last two. A right 

 understanding of these laws of organic modification, underlies 

 a right understanding of the great question of species. 

 While, as before hinted (§ 40), the action of structure on 

 function, is one of the factors in that process of differentiation 

 by which unlike forms of plants and animals are produced, 

 the re-action of function on structure, is another factor. 

 Hence, it is well worth while inquiring how far these induc- 

 tions are deductively interpretable. 



The first of them is the most difficult to deal with. Why 

 an organ exerted somewhat beyond its wont, should presently 

 grow, and thus meet increase of demand by increase of sup- 

 ply, is not obvious. We know, indeed, (First Principles, 

 §§ 96, 133,) that of necessity, the rhythmical changes pro- 



