154 HYPOTHESIS OF THE DEVELOPMENT OF 



be owned, equal proof that the tuskless hog of our farm-yards 

 is the same animal which roams the forest in formidable state 

 and armature, as that the wild boar is the same with the 

 domestic pig. 



It is difficult, after what has now been seen, to regard the 

 idea of species or specific distinction as descriptive of a fact in 

 nature ; it must be held as merely applicable to certain appear- 

 ances 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 observation 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 variabili- 

 ties are witnessed, even to the dissolution of genera among the 

 cryptogams and cereals, and the community of algas and fungi 

 water and land plants. Still, to keep the axiom whole, 

 these are held in doubt, or relegated to a place in the elastic 

 region of the varieties. Such is the stage which we have now 

 attained. But this is a process the reverse of philosophical : it is 

 to start with a theory, and then make facts succumb to it. 

 "Were the process reversed and the facts taken first, we should 

 see that a great modifiability exists in organic nature, espe- 

 cially in the humbler departments of the two kingdoms. 1 And 

 seeing that this modifiability presents itself within the scope 

 of a very limited experience, it might safely be inferred that 

 something much greater would be detected, if our range of 



* It is a very curious fact that, whilst the lower classes of living 

 beings are more capable than the higher of bearing the deprivation of 

 these vital stimuli, they are at the same time more liable to alterations 

 in their own structure and development, in consequence of variations in 

 the degree of the agency of these, and of other causes external to them- 

 selves. Thus the forms of the lower tribes of plants and animals are 

 liable to be greatly affected by the conditions under which they grow ; 

 and these also modify their degree of development. It seems as if the 

 formative power were less vigorous in the lower than in the higher 

 classes ; so that the mode in which it manifests itself in the former is 

 more dependent upon external influences ; whilst in the latter, it either 

 predominates over them, causing the regular actions to be performed, or 

 gives way altogether. The same principle applies to the early condition 

 of the higher organisms ; their ernbryoes, like those beings of perma- 

 nently-low type which they resemble in degree of development, being 

 liable to be affected by modifying causes, which the perfect beings of the 

 same kind are able to resist. Carpenter's General Physiology, 1851. 



