1884.] 
Theory of Evolution. 
191 
Again, we may take the case of the mule, ordinarily in- 
fertile. If its parents belong to one and the same species 
they ought to reproduce not merely a living, but a fertile 
offspring, If our opponents seek to get over this difficulty 
by pleading that the horse and the ass, though of the same 
species, belong to different races, they make the admission 
— ruinous to them — that there is no absolute difference 
between race or variety and species, the former being at least 
a stepping-stone to the latter. “ Ruinous,” I would say, 
because it in effedt involves the abandonment of their 
vaunted physiological characteristic of species as distindt 
from varieties. 
The second plea of the Cuvierians — if they will permit 
me to call them so — is not more valid than the first. 
Looking over the long list of cases above given, they say— 
“ But these are mere exceptions, and there is no rule with- 
out exceptions !” I am half inclined to suspedt that this 
very notion of exceptions to all rules is a proof of the radi- 
cally unscientific character of the minds which entertain it. 
I find in an important paper in the “ Deutsche Rundschau,” 
by Professor Preyer, of Jena, the following very significant 
remarks : — “The philologian only will refuse to admit that 
grammar, with its endless exceptions, is a heavy load for the 
memory rather than a discipline for the logical faculty. The 
student thus, almost involuntarily and unconsciously, learns 
to admit exceptions in the case of other rules, such as the laws of 
Nature .” Now in the rules or laws of Nature, when 
founded on a proper induction and clearly understood, there 
are no exceptions. If you can give us one instance of the 
destruction or the creation of matter, the so-called law of 
the permanence of matter falls at once to the ground, or is 
seen to be no law. If by any manipulation of ours we can, 
in any one case, create energy, the law of the conservation 
of energy must be forthwith given up. If one only of the 
elementary bodies of chemistry is found capable of com- 
bining with other bodies in fluctuating proportions, the 
atomic theory goes to the winds; and, just in the same 
manner, if we have one single instance of fruitful intercourse 
between animals of different species, the assumed law that 
such an event is impossible, and with it the physiological 
test of species, is annihilated, or rather is found never to 
have had a rightful existence. 
But the notion of “ no rule without exceptions,” idle as 
we have seen it to be, is capable of assuming a more ma- 
lignant phase. We sometimes hear it said that “ the 
exception proves the rule,” This floscule is most common 
