132 REV. JOHN GERARD, F.L.S., ON SPECIES AND THEIR ORIGIN. 
That species have no real existence naturalists who study 
living nature must, it would seem, find it exceedingly difficult 
to persuade themselves, so many and so far reaching are the 
points of resemblance which they must continually discover ; 
and which imperatively suggest the idea of a rule imposing 
them. If there be such a rule, then assuredly in a very true 
sense species are a reality, and the question of their fixity or 
transformation has a very definite meaning. If on the other 
hand, there be no such rule in existence, and the various 
characteristics in which classification of species is founded are 
due to fortuitous circumstances alone, then species owe their 
origin only to the men who invented them. And doubtless 
many species, especially amongst the smaller organisms, 
whether plant or animal, seem to be based on a foundation 
no more substantial. Professor Asa Gray, for instance, was 
known to say that he did not believe in the fixity of species, 
for he had made and unmade too many of them. But this 
means no more than that some which once he had called 
species were not in reality species at all; it nowise affects 
the case of “natural species,” if such there be, based upon 
characteristics common to individuals, and due not to fortuity 
but to law. 
There remains of course the perplexing question of the 
distinction between species and varieties and the test, or tests, 
by which species may practically be distinguished one from 
another—that most usually adopted being the impotence of 
creatures belonging to different groups to produce hybrids 
regularly fertile inter se. That this is a real test Professor 
Huxley at one time strenuously denied,* though at another 
he appeared to take it as the basis of his own conclusion 
on the subject. In any case it seems clear that groups 
which are recognised as true species do in certain circum- 
stances interbreed; for example, the black carrion crow 
(Corvus corone) and the grey hooded crow (Corvus cornia) 
undoubtedly do so on the borders of the districts which they 
respectively inhabit, and there can be no question that the 
offspring resulting from such unions are intermediate in 
plumage between the parents, and though it is not very easy 
in the case of such birds to obtain precise information, ib 
would appear that the hybrid race perpetuates itself. The 
same is the case with two species of goldfinch—Carduelis 
* The Darwinian Hypothesis, 1859, (Darwiniana, p. 3.) 
t+ The Origin of Species, 1860. (Lbid., p. 74.) 
