514 A NEW THEOEY OF THE ORIGIN OF SPECIES. 



His doctrine consists, as might be anticipated from wliat ^ve have 

 said, in the denial of gradual ti'ansformatidh and the affirmation of 

 abrupt transformation. Species in general do not enjoy that per- 

 fectly" uniform and monotonous existence which has been assigned to 

 them by naturalists of the school of Linnivus and Cuvier. Paleontol- 

 ogy teaches us that the}" have a commencement and an end and that, 

 during their term, they present periods of two kinds, periods of muta- 

 tion and periods of equilibrium, times of calm and times of revolution. 

 The observation of existing species contirms this view. 



Ordinaril}" the principal '"period of mutation " is found at the earliest 

 stage of the species, at the time of its birth, but this is not absolute. 

 However, the phase, or the entire group of phases, of plasticity, is 

 more or less brief in comparison with the rest of its existence. It is 

 only at these epochs that the living being is susceptible of mutations 

 of a specific character; it is unchangeable for the rest of the time, that 

 is to say, during the greater part of its term. Because of this the 

 period of plasticity or of mutation usualh' escapes attention and we 

 observe the greater number of species exacth^ at the moment when 

 they have become really invarial^le — that is to say, susceptible only of 

 those small, secondary modifications which may, at most, conduce to 

 the formation of varieties and races. 



When, on the contrary, the species is in the period of mutation it 

 oti'ers an abundance of specific variations, distinct in character from 

 the small, individual ones. They are, in fact, abrupt, clearly marked, 

 permanent, fixed, and hereditary as soon as they appear, and the new 

 forms are infertile when crossed on the parent stock. In a word they 

 accomplish a transgression of the limits of a species. 



Such is the new hvpothesis of nmtation. Before detailing the exper- 

 iments on which it is founded, and furnishing the justification of its 

 accuracy, it would be well to establish its signification, its scope, and 

 its consequences. 



This theory- is a sort of rehabilitation of the idea of species. It does 

 not, liowever, consider species as the fixed entity, the special and 

 innnuta])le category of the Creator's thought, conceived by the natural- 

 ists who followed Linna?us. It is trulv a transfoi'mist doctrine; it 

 admits the possible existence of an infinite number of species derived 

 one from the other. Nevertheless it must not be denied that it confers 

 on species an ol)jt'ctive existence, a sort of reality that is foreign to 

 the conception of the transformist school. *' Species appear," says 

 Hugo de Vries, "like invariable unities, such as are necessary in a 

 systematic classification. Their existence is real, like that of individ- 

 uals. A species is born, has a short period of youth during which it 

 is subject to specific mutation, is maintained in an adult condition 

 during a period which mav ^>e of great length, then finally disappears." 



The doctrine of Hugo de Vries is opposed to that of Darwin in 



