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CHAPTER XXXIT. 



FERTILISATION AND THE ORIGIN OF SPECIES. 



The Origin of Species by Insect Agency. — The attractive 

 features of flowers being now well recognized as correlated 

 with insect agency in fertilisation, the question arises, How 

 have they come into existence ? We may suppose that a plant 

 bore seedlings, some of which had, we will say, the corolla 

 accidentally (that means from some unknown cause arising 

 from ivithin) larger on one side than another ; and then such 

 a flower, being selected by insects, left offspring which, by 

 gradual improvement through repeated selection, ultimately 

 reached the form it now possesses. 



As an alternative, we may suppose that the first impulse 

 came from without, and induced by the insect itself ; so that 

 the variation once set up in a definite direction, went on 

 improving under the constantly repeated stimulus of insect 

 visitors until the form of the flower was actually con- 

 formable to the insect itself. 



The process of evolutionary development might perhaps 

 be much the same under either supposition, but the latter 

 hypothesis has more than one advantage. First, in the 

 assignment of a direct physical cause for the incipient change, 

 instead of some incidental and unaccountable variation, 

 which must be assumed by the former. Secondly, the theory 

 does not require the plant to make an indetinite number of 



