INHERITANCE IN HYBRIDS. 211 



transmission. It alone, wlien rightly estimated, is quite 

 sufficient to refute the prevailing dogma of the constancy 

 of species. Plants, as well as animals, belonging to quite 

 different species, may sexually mingle with one another 

 and produce descendants which in many cases can again 

 propagate themselves, and that indeed either (more fre- 

 quently) by mingling with one of the two parental species, 

 or (more rarely) by pure in-breeding, hybrid mixing with 

 hybrid. The latter is well established, for example, in the 

 hybrids of hares and rabbits (Lepus Darwinii, p. 147). The 

 hybrids of a horse and a donkey, two different species of 

 the same genus (Equus), are well known. These hybrids 

 differ according as the father or the mother belongs to the 

 one or the other species — the horse or the donkey. The 

 mule produced by a mare and a he-donkey has qualities 

 quite different from those of the jinny (Hinnus), the hybrid 

 of a horse and she-donkey. In both cases the hybrid pro- 

 duced by the crossing of two different species is a mixed 

 form, which receives qualities from both parents ; but the 

 qualities of the hybrid are different, according to the form 

 of the crossing. In like manner, mulattoes produced by 

 a European and a negress show a different mixture of 

 characters from the hybrids produced by a negro with a 

 European female. In these phenomena of hybrid-breed- 

 ing, as well as in the other laws of transmission pre- 

 viously mentioned, we are as yet unable to show the acting- 

 causes in detail ; but no naturalist doubts the fact that the 

 causes are in aU cases purely mechanical and dependent 

 upon the nature of organic matter itself If we possessed 

 more delicate means of investigation than our rude organs 

 of sense and auxilliary instruments, we should be able to 



