66 ON VAlliETlES, liACES, SUB-SPECIES, AND srEClES. 



the answer given by those who, like M. Cuvier, recognize suc- 

 cessive creations of organized beings corresponding to certain 

 revolutions of the globe. But it is as well to observe, that these 

 successive creations are not a necessary consequence of tlie immu- 

 tability of species ; for M. de Blainville, who entertained this 

 opinion in its fullest extent, only admitted one single creation of 

 organized beings, 



Some gardeners and farmers have declared, that good varieties 

 of fruit trees propagated by the division of an individnal, on 

 having recourse to layers, budding or grafting, degenerate after 

 having lived a certain time, and that plants propagated by scales 

 and otherwise do the same ; in support of this opinion tliey quote 

 the disappearance or death of a great number of varieties of vines, 

 apples, pears, &c., v/hich have been described by Pliny, Olivier 

 de Serres, La Quintinie, cfec. This opinion, v/hich, as we have 

 already said, does not appear to us to be founded, at least to the 

 extent to which certain contemporaries, and more especially M. 

 Puvis, have carried it, might nevertheless be true, and yet the 

 mutability of species need not necessarily result from it. To 

 this, however, we shall revert in another Part of this essay, 

 which will, we hope, serve as a supplement to the preceding re- 

 marks, and as a justification of the line we have adopted in treat" 

 ing of a subject, the importance of which is only equalled by its 

 difficulties. 



However weiglity the second thing which we have regarded 

 in a species may be, it unfortunately occupies very little space 

 in the domain of positive science ; for we possess scarcely any 

 facts, either of experiment or mere observation, which at all show 

 the exact influence of the external world on the organic consti" 

 tution of individuals, and the few^ facts we have, apply to a 

 small number of individuals of a still smaller number of species. 

 And liow can it be otherwise when we reflect on the difficulties 

 which must be encountered, and the slowness with whicli organ- 

 ized beings can be modified in a series of generations which last 

 mucli longer than the life of the observer? The small number 

 of scientific men who occupy themselves with such inquiries as 

 these, belong to the class of natural physiologists, who, from the 

 very nature of their pursuits, are more inclined to devote them- 

 selves to such studies than naturalists, more properly so called. 



■ Conclusions relatiny to the definition of species, 



1. In the actual state of our knowledge, the facts relating to 

 the first thing in the notion of species, and of whicli the greater 

 part result from tlie daily observation of the reproduction of ani- 

 mals and plants, are in favour of tlie opinion of the immutability 

 of species; for, however great the variation observed in indivi- 



