No doubt, it is logically unjustifiable to argue from the 

 variable concept to the variability of the species. Still 

 there is something real in plants and animals which corre- 

 sponds to our specific concepts. In some cases the corre- 

 sponding reality may' be so well defined that it is not diffi- 

 cult to form the concept accurately; whereas in other cases 

 where the task is more difficult, the difficulty must be due 

 to the object. Under these circumstances we may safely 

 conclude from the lack of definiteness in our concepts to 

 a certain lack of rigid delimitation in the organic forms. 



This blending of certain forms suggests the idea of 

 transformation, but does not furnish definite proof of it. 

 Such proof can be had only by the direct observation of a 

 transformation. And no doubt in certain cases a transfor- 

 mation may occur. As regards animals, I may call atten- 

 tion, for instance, to the experiments made with butterflies 

 by Standfuss, and as regards plants, to the experiments of 

 Haberlandt, of which I treated in Chapter III. The limits 

 within which these transformations take place are indeed 

 very narrow as are also the limits of those indisputable va- 

 rieties which naturally arise within an otherwise rigidly 

 defined species. I am aware that the transformation of one 

 species into another has not yet been effected, but the 

 above-mentioned attempts at transformation have never- 

 theless demonstrated that certain organic forms when sub- 

 jected to changed conditions of life, display certain muta- 

 tions which clearly show that variabiHty is to be attributed, 

 not, certainly, to the specific concepts, but to the corres- 

 ponding reality. This observation and reflexion, joined 



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