and Nature of Specific Distinctions. 511 



dry skin is hardly sufficient on which to found a definite 

 opinion. 



Of course, all these various facts lead us to the important 

 consideration of, What is a species ? What constitutes specific 

 distinction ? To which the only rational reply appears to be 

 (and even this is quite incapable of probation), Beings derived 

 from a separate origin. For it appears that hybridism, after 

 all, is but an uncertain guide, however satisfactory in particular 

 cases ; there being much reason to conclude, from a general 

 survey of the facts recorded, that, as the degree of fertility in 

 hybrids (paired with individuals of pure blood) varies ac- 

 cording to the degree of proximity in the parent species, the 

 possibility of mules being produced at all existing only within 

 the sphere of a certain affinity ; so, on the other hand, when 

 the parent species approach so nearly as some that I have had 

 occasion to mention, their mixed offspring would be almost 

 equally prolific, hybrid with hybrid. This'is, at least, stated 

 of all the members of the genus Bos ; and most naturalists 

 concur in the opinion, that our common fowls are derived 

 from the blending of a plurality of species. Certainly, if the 

 analogy of plants can be admitted, the fact is in so far settled ; 

 for I know many hybrid plants which of themselves yield 

 fertile seed in abundance : the mixed produce, for example, 

 of the Calceolaria purpurea and C. j^lantaginea ; the former 

 a half-shrubby species, the latter herbaceous.* A variety 

 of additional instances could be enumerated. Hybrid plants, 

 however, are equally sterile with mule animals, if the parent 

 species are not very closely allied. 



It is to be hoped that, ere long, the experiments of the Zoo- 

 logical Society will have solved this curious and important 

 problem. Already some highly interesting and complex hy- 

 brids have been obtained under their management, f 



* It is greatly to be wished that horticulturists would not name their 

 hybrid plants in the same manner as genuine species ; the confusion thus 

 already induced in many genera being quite inextricable. Surely they 

 could find some other mode of denoting them. 



f Since writing this, I have ascertained the fact, that the mule progeny 

 of the A'nser cygnoides, coupled with the domestic goose, breed freely 

 with one another ; and have seen an individual of which both the parents 

 were hybrids. We do not, indeed, know the wild stock of the domestic 

 goose ; but, certainly, no one would dream of referring it to A. cygnoides. 

 As Mr. Jenyns well observes, the common gander, after attaining a certain 

 aire, is always white, a character which, it may be remarked, is in accordance 

 with the snow goose (A. hyperboreus) of North America, a species obvi- 

 ously distinct. Let it be, however, borne in mind, that, in every known 

 instance, intermixture of species is solely induced by man's agency ; even 

 the mules that have been found wild between Tetrao Tetrix and Phasi- 

 anus colchicus : for instance, White of Selborne, who figures one of these, 



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