[April, 
i go Hybridism with Reference to the 
three groups which have come most extensively and closely 
under human observation, — to wit, the poultry tribe, the 
geese and ducks, and the finches and thrushes. It is surely 
therefore reasonable to expeCt that if other families of birds 
were submitted to similar investigation, the number of 
affirmative instances would be increased. I may safely say 
that not one species in a thousand has been examined so 
closely that we can say with anything like confidence 
whether it is capable of reproduction with some allied spe- 
cies or not. If we observe animals in a state of nature we 
may, perhaps, not find a crucial instance once in a quarter 
of a century. If we experiment upon them in captivity we 
are met by the difficulty that many animals do not breed 
freely in confinement, even when mated with one of their 
own species. Differences of temperature, of diet, of exer- 
cise, of exposure to light, and a variety of other circum- 
stances not capable of affecting the health of an adult 
animal, may yet prevent it from breeding, or may prove 
destructive to its young. For anything we can show to the 
contrary many existing species may have had their origin in 
hybridisation. 
Let us now discuss some of the arguments used to explain 
away, if possible, the faCts which have been brought forward. 
We hear it sometimes said that if two animals are capable 
of engendering together they must belong to the same spe- 
cies. If this assertion is valid, then the horse, ass, and 
zebra are merely different races of one and the same species. 
So, too, are respectively the American bison and the com- 
mon cow ; the dog, wolf, and fox ; the lion and the tiger ; 
the hare and the rabbit ; the hoodie and the carrion crow ; 
the blackbird and the thrush ; and multitudes of other spe- 
cies differing from each other in form and in habits. In 
short, to preserve a dogma, for it is nothing more, the 
classification of the animal — and in like manner of the vege- 
table — world is to be thrown in heaps. This plea is, in 
short, an excellent instance of the working of the principle 
tant pis pour les faits ! But we may take another step. 
Suppose that the copulation of two animal forms, ordinarily 
held to be distinct, leads, not indeed to the birth of living 
young, but to the earliest stage of conception, or, in tech- 
nical language, to the segmentation of the ovum, what are 
we then to conclude ? Do the two animals belong to one 
and the same species ? If they do, they ought to be capable 
of producing viable young. If they do not, then, according 
to the creed of the past, their intercourse should be utterly 
null and void. 
