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vades the former territory of another. In our own country, for 
example, the grouse gives way to the partridge, or the snipe to the 
landrail; or, more rarely, the lark may be supplanted by the waders and 
the gulls— the field-mouse and the mole by the water-rat and the otter. 
But in no case that we know of, or that Mr Darwin has adduced, has 
any wild animal been enabled, by any modification of form, however 
slight, to survive any essential changes in that condition for which it 
was first adapted. And as this is the law which obtains in the present, 
so also it is the law which appears to have obtained in the past. The 
absence of any evidence of the passage of one form into another, dis- 
coverable in the records of former worlds, is confessed by our author 
himself. All his arguments are directed, not to deny this fact, but to 
explain it. It has been truly said, in a very able and interesting paper 
on the subject which was communicated to this Society by one of its 
members early in the present year, that “The strongest points in favour 
of the general results come to by Mr Darwin, are a class of facts which 
can scarcely be said to bear distinctively on his theory more than 
upon various other theories already promulgated, and more or less 
adopted. One of these is the fact that all animals and plants, 
throughout all time and space, should be related to each other in 
group subordinate to group, another not less formidable 
fact is the existence of the same homological parts in different 
animals, sometimes aborted, and sometimes largely developed.” 
The endeavour to explain and account for these strange connections 
and relationships is one of the highest aims of science. To refer 
them to the great law of hereditary descent is a very natural sugges- 
tion, and for a moment some minds may be disposed to rest in it as 
a kind of explanation. Reduction to a known and familiar law is 
the nearest approach to explanation which science can afford. But 
we must beware of the subtle error which lies in changing a law 
well known and familiar, into another law entirely unknown and 
new, by ascribing to it effects and operations of which we have no 
experience. If the law of descent by ordinary generation is con- 
sistent with the origin, through this means, of new species, some 
proof must be given of the fact. Until such proof is adduced, the 
assumed law is not that of ordinary generation, but of extraordi- 
nary — of a new kind of generation essentially different from that of 
which we have any knowledge. 
It is well worthy of remark, that Mr Darwin holds strongly to the 
