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case under illustration, is undoubtedly a serious difficulty in 
the way of the acceptance not only of the Darwinian theory, 
but of any doctrine of evolution. Any such doctrine, if it is to 
he applied universally , must stand by Mr. Wallace’s law, that 
“ every species has come into existence, coincident, both in space 
and time, with a pre-existing closely-allied species.” This 
statement of the case, as I have elsewhere pointed out, is ob- 
viously too wide, since, even from the evolutionist’s point of 
view, we must somewhere come to a point where the organisms 
(or organism) in existence had no pre-existent types. It is 
certain, however, that no doctrine of general evolution can 
afford to admit the sudden appearance of new specific or 
generic types in time. From all that palaeontology teaches us, 
on the surface at any rate, such new types have constantly been 
coming into existence in past time, as we have just seen; and 
it is not easy to discover any satisfactory explanation of this 
troublesome fact. The most obvious way of evading the diffi- 
culty, and the one which Mr. Darwin has adopted, is to assert 
that what appears to us to be the first appearance of new generic 
or specific types is only due to the imperfect state of our know- 
ledge, and that the said types were really in existence long 
before the period of the formation in which we first find them. 
In such cases as concern the first appearance of given types in 
given areas, and in which it can be shown that similar or nearly 
allied types have existed in other areas in older formations, there 
is a strong probability that this explanation is correct, and that 
what we call “ first appearance ” is merely an instance of “ migra- 
tion.” When this assertion, however, ismade asa^eneraZstatement, 
applying to the general phenomenon of the sudden appearance 
of new specific and generic types throughout the entire series 
of the stratified rocks, then two things are clear. — Firstly, that 
such an assertion is only an assertion, which, even if probable, 
would ever remain improvable; and secondly, that such an 
assertion is in the highest degree improbable, though its falsity 
likewise does not admit of positive proof. That in many cases, 
the points where we now note the first appearance of generic 
and specific types in the geological record, are not the actual 
points at which they were first introduced upon the scene, 
either as regards time or space, is likely enough. But, that 
this is true of all the new species and genera that have made 
their appearance upon the earth since the commencement of 
the Cambrian epoch, is not only an assumption, but it is one 
that can only be sustained by making other assumptions 
equally unsupported by definite proofs. And it may be noted 
here, that to derive any benefit from this argument, it is neces- 
