They must
rather have disappeared again as they arose, and the lists would remain
open to the males under variation, only in respect of their sexual
relations. In these they might acquire advantages over their rivals by
their being enabled either to seek or to seize the females better. The
best smellers would overcome all that were inferior to them in this
respect, unless the latter had other advantages, such as more powerful
chelae, to oppose to them. The best claspers would overcome all less
strongly armed champions, unless these opposed to them some other
advantage, such as sharper senses. It will be easily understood how in
this manner all the intermediate steps less favoured in the development
of the olfactory filaments or of the chelae would disappear from the
lists, and two sharply defined forms, the best smellers and the best
claspers, would remain as the sole adversaries. At the present day the
contest seems to have been decided in favour of the latter, as they
occur in greatly preponderating numbers, perhaps a hundred of them to
one smeller.
To return to Bronn's objection. When he says that "for the support of
the Darwinian theory, and in order to explain why many species do not
coalesce by means of intermediate forms, he would gladly discover some
external or internal principle which should compel the variations of
each species to advance in ONE direction, instead of merely permitting
them in all directions," we may, in this as in many other cases, find
such a principle in the fact that actually only a few directions stand
open in which the variations are at the same time improvements, and in
which therefore they can accumulate and become fixed; whilst in all
others, being either indifferent or injurious, they will go as lightly
as they come.
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