Ci:\v. Vlil. lIYBiaDISM. 23J 



CHAPTER VIII. 



IIYBKIDISM. 



Distinction Ijctwpon the Stcrilifir of First CropfCF and of Hybrids— Slorilil.v various 

 in JX'iXTCf, nut uiiivtM>jil. all'i'ctcd l)y cIojji! Interbrccdincr, removed by Domesti- 

 cation— Lawf LTovi'miiiL,' llie Sterility of Hybrids— Sterility not a special Endow- 

 ment, bat incidental on oilier DilTerences, not accnmiilated by Natural Selection 

 — Causes of the Sterility f)f First Crosses and of Hybrids— i'urallilisrn between 

 llie Ell'ectrt of Clianjred Conditions of Life and of Crossin;,'— Diinnrnldsm and 



, Triuiorpliism — Fertility of Varieties when crossed and of their Monjirel Ollsprinij 

 not universal— Hybrids and Mongrels compared independently of tlicir Fertility 

 —Summary. 



The view generally entertained by naturalists is that 

 species, when intercrossed, have been specially endowed witli 

 sterility, in order to prevent their confusion. This view cer- 

 tainly seems at first hifi;hly pro])able, for s])ecies within the 

 same country could hardly have been kept distinct had they 

 been capable of freely crossing-. The subject is in many ways 

 important for us, more especially as the sterility of species 

 when first crossed, and that of tlieir hybrid offspring, cannot 

 have been acquired by the continued preservation of successive, 

 ]irolit:d)lc degrees of sterility. It is, as I hope to show, inci- 

 dental on differences in tlie reproductive system of the jiarciit- 

 spceics, and is not cither a specially acquired or endoAVcd 

 quality. 



In treating this subject, two classes of facts, to a large ex- 

 tent fundamentally different, have generally been confounded 

 together ; namely, the sterility of two species when first crossed, 

 antl the sterility of the hybrids produced from them. 



Pure species have of course their organs of reproduction in 

 a perfect condition, yet when intercrossed they produce either 

 few or no offs])ring. Hybrids, on the other hand, have their 

 reproductive organs functionally impotent, as may ])e dearly 

 seen in the; statt; of the malt; element in both ])hints and ani- 

 mals ; though the formative; organs themselves are perfect in 

 structure, as far as the microscope reveals. In the first case 

 the two sexual elements which go to form the embryo are per- 



