DEFINITION OF SPECIES. 19 



The definition of species, as given by Cuvier, 1 seems to have 

 been generally accepted in natural history. " To the same 

 species belong all such individuals which have descended from 

 each other or from common parents, and from those who re- 

 semble them as much as they resemble each other." 



Prichard's definition that the term species includes separate 

 origin and constant transmission of organic peculiarities, is 

 identical with that of Cuvier. Though this definition is theo- 

 retically unquestionable, it contributes little or nothing to the 

 solution of the practical question with regard to the characters 

 by which individuals of the same species may be distinguished 

 from others belonging to a different species ; for the difficulty 

 to be solved is, to establish a decisive character for the great 

 majority of cases in which we know nothing of descent, and in 

 which the resemblance of the individuals is less than that gene- 

 rally subsisting between parents and children, and individuals 

 of the same stock. For such a character, definitions are re- 

 quired which can be confirmed or refuted by experience ; but 

 this, as regards common descent, excepting individual in- 

 stances, is not the case, for in respect to remote generations 

 more or less probable suppositions are only possible. To this 

 defect may be added another of still greater importance. 



Though we may readily grant that unity of species results 

 from unity of descent, and though in the study of zoology and 

 descriptive natural science unity of descent is chiefly con- 

 sidered, as it treats of the propagation and history of organ- 

 ized beings, still it is a confusion of terms to identify the notions 

 of unity of species and unity of descent, which according to the 

 above definition is frequently done even by Prichard, who con- 

 siders separate descent and original differences of character as 

 convertible terms. In spite of this frequent confusion of 

 terms, he observes, very justly, that the term species should 

 only be applied to an aggregate of individuals, where nothing 

 intervenes to consider them as the descendants from the same 

 stock : that is to say, when we are not obliged to reduce them 



1 " La reunion des individus descendus Tun de 1'autre ou de parents com- 

 muns, et de ceux qui leur ressemblent autant qu'ila se ressemblent entre eux." 

 Kgne Animal, 2nd edit., i, p. 16. 



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