46 



of a large number of specimens from different localities. T do 

 not use the word species as the type of a group of allied 

 organisms which have a rigidly determinate number of 

 immutable characteristics in common ; for the characters 

 which, as a whole, are relatively constant in those 

 sections which we group under a specific name are themselves 

 variable, and are frequently to be found interlapping 

 other groups of merely relative constant characters, but which 

 we yet acknowledge as belonging to a distinct species. From 

 long and close observation Oscar Schmidt* concludes 

 that he has gradually arrived at the "conviction that no 

 reasonable dependence can be placed on any ' characteristic ' ; 

 that with a certain (Constancy in microscopic constituents the 

 outward bodily form, with its coarser distinctive marks, varies 

 far beyond the limits of the so-called species and genera ; and 

 that with like external habits the internal particles, which we 

 look upon as specific, are transformed into others, as it were, 

 under our hands." There is, consequently, a firm conviction 

 in the minds of leading naturalists " that no absolute species 

 exists, and that species and varieties cannot be sharply sepa- 

 rated." The old idea of the immutability of species is no 

 longer tenable. Many still treasure up certain old test measures 

 for the purpose of determining the affinity of a doubtful 

 species — such, for example, as the fertility of certain crosses — 

 fertility or non-fertility of hybrids. But such tests, in the 

 light of modern experience, are unsatisfactory and often 

 deceptive. 



Darwin, Haecke], and others have demonstrated the fallacy 

 of trusting too much to such tests, and Schmidt writes : — 

 " It is known that even in a state of freedom good 

 species, such as the horse and ass, have been crossed 

 for thousands of years. But hybrids, the produce of 

 this intercourse, were supposed to be only exceptionally fertile, 

 and, at any rate, not to produce fertile progeny for more than 

 a few generations. On the other hand it was considered 

 certain that the produce of crosses among varieties are fertile 

 in unbroken succession. The dogma of the sterility of hybrids 

 was formed without experimental or general observation, and 

 by ill-luck was apparently confirmed by the most ancient and 

 best known hybridization of the mule andhinny. To this familiar 

 example, in which the fertility of hybrids proves abortive, we 

 will oppose only one case of propagation successfully accom- 

 plished in recent times through many generations — that, 

 namely, of hares and rabbits, two good species, never yet 

 regarded as varieties." The same writer, after quoting 



*" Doctrine of Descent and Darwinism. 1875," 



