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irregular, uncertain, or even wanting. Caterpillars are 
provided with beautiful protective adaptations, but the suc- 
cessful individual never comes into contact with an enemy. 
But there is an environment which the organism cannot avoid, 
—the physico-chemical stimuli of climate and food ; and it is 
presumably here, in the inorganic conditions of life, that the 
influences which bear a pre-eminent part in evoking useful 
variations are supposed to reside. So that stimuli provided 
by one form of environment are looked upon as the direct causes 
of adaptations which are essentially related to another and 
very different environment. * 
The Instincts of Insects —Those who advocate the hereditary 
transmission of acquired characters have made great use of 
the argument that the wonderfully complex and precise 
adaptive instincts of insects require for their production the 
accumulation of experience and of effort through many 
generations. Only by such transmission, they maintain, is it 
possible to understand such development. 
It is safest to begin with a definition, and I accept the brief, 
convenient and in my opinion entirely accurate statement of 
Lloyd Morgan:—“ Instinct depends on how the nervous system 
is built through heredity ; while intelligence depends upon 
how the nervous system is developed through use.” f 
We observe in the first place that the Lamarckian interpreta- 
tion places the more difficult phases of the evolution of instinct 
—the phases when it was not instinct at all but something 
much higher—in some remote epoch of the past, and at a lower 
level of progress. In such times, ex hypothesi, the less developed 
and presumably less efficient brains of insects did by the 
intelligent use of experience what they now do mechanically 
by instinct. This is an inversion of the probable course of 
evolution: the less efficient instrument has assigned to it by 
far the more difficult task. 
Apart from this primd facie objection there are solid 
grounds for the belief that the exquisitely perfect operations 
of insects with which we are familiar arose as instincts, as 
* The substance of the argument set forth in this paragraph was 
published by the writer in ‘‘ Nature,” vol. 1, 1894, p. 445. 
+ “ Animal Behaviour,” London, 1900, p. 120. 
