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creature, yet there must be some limit to their number; and it 
appeal's natural that gemmules derived from an enfeebled and useless 
rudiment would be more liable to perish than those derived from 
other parts which are still in full functional activity.”—(The Variation, 
vol. ii., pp. 397-8.) 
Mr. Wallace, in the following passage, seems to recognise 
the co-operation of various causes to produce abortion. 
“ On a review of the various examples that have been given by 
Mr. Darwin and others, of organs that have been reduced or aborted, 
there seems too much diversity in the results for all to be due to so 
direct and uniform a cause as the individual effects of disuse accumu 
lated by heredity. For if that were the only or chief efficient cause, 
and a cause capable of producing a decided effect during the com 
paratively short period of the existence of animals in a state of 
domestication, we should expect to find that, in wild species, all 
unused parts or organs had been reduced to the smallest rudiments, 
or had wholly disappeared. Instead of this, we find various grades 
of reduction indicating the probable result of several distinct causes, 
sometimes acting separately, sometimes in combination, such as those 
we have already pointed out.”—(Darwinism. pp. 416-17.) 
It is obvious, then, that, according to the teaching of the 
most eminent exponents of Darwinism, there are forces at 
work in nature tending to produce degeneration of organs, 
altogether apart from Natural Selection. But of course it 
is maintained that Natural Selection has exercised a great 
influence also. This conviction is based upon the severe 
struggle for existence, in consequence of which an animal 
cannot afford to support an organ functionally useless, or 
even to nourish a rudiment, however small. 
“ Natural Selection is continually trying to economise every part of 
the organisation. If, under changed conditions of life, a structure, 
before useful, becomes less useful, its diminution will be favoured, for 
it will profit the individual not to have its nutriment wasted in building 
up an useless structure. . . . 
“The saving of a large and complex structure when rendered 
superfluous, would be a decided advantage to each successive indi 
vidual of the species ; for in the struggle for life to which every 
individual is exposed, each would have a better chance of supporting 
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