THE VEGETABLE AND ANIMAL KINGDOMS. 137 



differences greater than what are usually regarded as suffi- 

 cient to constitute species. But the most striking observations 

 on this subject are those of M. Roulin, made during a resi- 

 dence of several years in Columbia, relative to the races which 

 had been introduced there in a domesticated state by the 

 early voyagers, and allowed to run wild during the three 

 centuries which have since elapsed. As an example, the hog : 

 " Wandering all day in the woods, this animal has lost nearly 

 all marks of servitude ; its ears have become erect, its head 

 broadened, and raised at the upper part, and its colour has 

 been rendered permanent." It has, in short, returned to a 

 strict resemblance to the wild boar of France. The cow, also, 

 from the cessation of the practice of milking, has lost the 

 abundant flow of milk which is found in her species in 

 Europe : to get milk from her at all, it is necessary that her 

 calf should be left with her. M. Roulin arrived at the fol- 

 lowing conclusions : that animals naturalized in new countries 

 undergo durable changes, bringing their organization into 

 accordance with the climates in which they are destined to 

 live ; and that habits of independence soon make the domestic 

 species resume the characters of the wild species from which 

 they have sprung. We have here, it will be owned, equal 

 proof that the tuskless hog of our farm-yards is the same 

 animal which roams the forest in formidable state and arma- 

 ture, as that the wild boar is the same with the domestic pig. 

 It is difficult, after what we have now seen, to regard the 

 idea of species or specific distinction as descriptive of a fact 

 in nature ; it must be held as merely representing certain 

 appearances presented, perhaps transiently, to our notice. 

 The history of the question seems to be this. Naturalists, 

 starting with a limited fund of observation, mainly, indeed, 

 consisting of the remark which the most superficial observa- 

 tion supplies, that like usually produces like, lay it down as 

 an axiom that species is a determinate thing. In a little time, 

 certain modifiabilities are observed. To maintain the axiom 

 intact, these are called varieties. Afterwards, much greater 

 variabilities are witnessed, even to the dissolution of genera 

 among the cryptogams and cereals, and the community of 



