HYBRIDS 133 



declared, as we stood in front of the specimen of the 

 Okapi of the Congo Forest, that it was clearly a hybrid 

 between the giraffe and the zebra. He insisted that it 

 was obvious that such was its explanation, and pointed 

 to its striped haunches and legs, and its cloven hoofs 

 and giraffe-like head. I failed to change his opinion. 



It is the fact — ascertained by careful observation of 

 natural occurrences and by experiment — that, in spite 

 of the almost absolute law or general truth to the effect 

 that the members of a species (whether of plant or 

 animal) only produce fertile offspring by mating with 

 members of that same species, yet there are rare instances 

 known in which individuals of two distinct but allied 

 species have mated and produced fertile offspring. The 

 cases in which such unions have resulted in the production 

 of offspring, but in which the offspring so produced prove 

 to be infertile — that is, incapable of producing offspring 

 in their turn — are much more numerous. An important 

 distinction has also to be made between cases of either 

 fertile or infertile hybrid-production which occur spon- 

 taneously in nature, and those in which man by separating 

 the parent animals or plants from their natural con- 

 ditions of life, or by bringing about impregnation (as in 

 " pollinating " one flower with the pollen-dust of another) 

 succeeds in obtaining a " cross " or " hybrid," whether 

 fertile or infertile, not known to occur in " wild " (that 

 is, not humanly controlled) nature. The rarest case 

 would be that of the production of fertile hybrids in 

 uncontrolled natural conditions. Such possibly occur in 

 the case of some fishes in which the fertilization of the 

 eggs takes place in water, the fertilizing microscopic 

 sperms passing from the males like dust into the water and 

 thus reaching the eggs laid by the females. Occasionally 

 hybrids are thus produced between some common fresh- 

 water fishes — species of the same genus — and between 



