ON VARIETIES, rvAOES, SUB-SrECIEb, AND srECIES. 67 



duals of the same species may be, no one of these individuals 

 has ever been found which belonged to a species diiferent from 

 that of its parents, or which constituted a new species. As we 

 have already stated, every -day observation, and experiment de^ 

 monstrate, so far as the circumstances of our own days 

 ARE CONCERNED, thc permanence of the types which constitute 

 the species of living bodies. 



2. But is this conclusion sufficient to authorize us to say, that 

 in different circumstances, species which actually exist could 

 never be so modified as to produce individuals which, compared 

 with those we at present know, would form different species ? 

 We think not. But, admitting that as the matter now stands, 

 we cannot affirm that it is absurd to think that a species could 

 not undergo modifications capable of making a new species ; on 

 the other hand, to admit the principle of mutability of species 

 would be to derogate from the rules of experimental method, 

 inasmuch as all the facts at present known do not favour this 

 opinion. In short, if the opinion of the mutability of species^ 

 under circumstances different from those under lohich we noto 

 live, does not appear absurd, to admit the fact in order to draw 

 consequences from it, is to depart from the strict principles of 

 experimental inquiry, which never permit us to lay down that as 

 a principle which is matter of mere conjecture. 



3. Although we allow the possibility of the mutation of 

 species within certain limits, by circumstances depending on the 

 exterior world, we do not infer either tlie non-existence of species 

 or the uselessiiess of the studies of those who attempt to 

 define them : for we adopt the definitions of species given with 

 exactness by those naturalists who believe in their absolute 

 immutability, but \n ho have observed with certainty, in a series 

 of generations, the recurrence of those characters which are 

 essential to each of them ; in our view, however, these definitions 

 are only true, are only exact, for the circumstances in which the 

 species habitually live. 



Having stated the preceding conclusions, we will point out in 

 what way error, or want of precision, may exist in the definition 

 of species by botanists and zoologists, taking for the date of their 

 origin the period at which they received the form which we now 

 see, whether in reality they do or do not go further back than 

 that. "We think a species is well defined in principle, when the 

 individuals which now represent it resemble their most ancient 

 ancestors. 



Errors. 



The errors found in the definitions given oi species insLy have 

 arisen from the carelessness or want of knowledge of their 



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