INHERITANCE IN HYBRIDS. 211 
transmission. It alone, when 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 all 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 
