220 MISCELLANEOUS OBJECTIONS TO THE 



stimuli, they are excited in an incidental manner by a touch 

 or by being shaken. Hence there is no great difficulty in 

 admitting that in the case of leaf-climbers and tendril-bear- 

 ers, it is this tendency which has been taken advantage of 

 and increased through natural selection. It is, however, 

 probable, from reasons which I have assigned in my memoir, 

 that this will have occurred only with plants which had 

 already acquired the power of revolving, and had thus 

 become twiners. 



I have already endeavored to explain how plants became 

 twiners, namely, by the increase of a tendency to slight and 

 irregular revolving movements, which were at first of no use 

 to them; this movement, as well as that due to a touch or 

 shake, being the incidental result of the power of moving, 

 gained for other and beneficial purposes. Whether, during 

 the gradual development of climbing plants, natural selection 

 has been aided by the inherited effects of use, I will not 

 pretend to decide ; but we know that certain periodical 

 movements, for instance the so-called sleep of plants, are 

 governed by habit. 



I have now considered enough, perhaps more than enough, 

 of the cases, selected with care by a skilful naturalist to 

 prove that natural selection is incompetent to account for 

 the incipient stages of useful structures ; and I have shown, 

 as I hope, that there is no great difficulty on this head. A 

 good opportunity has thus been afforded for enlarging a 

 little on gradations of structure, often associated with strange 

 functions — an important subject, which was not treated 

 at sufficient length in the former editions of this work. I 

 will now briefly recapitulate the foregoing cases. 



With the giraffe, the continued preservation of the indi- 

 viduals of some extinct high-reaching ruminant, which had 

 the longest necks, legs, etc., and could browse a little above 

 the average height, and the continued destruction of those 

 which could not browse so high, would have sufficed for the 

 production of this remarkable quadruped ; but the prolonged 

 use of all the parts, together with inheritance, will have 

 aided in an important manner in their co-ordination. With 

 the many insects which imitate various objects, there is no 

 improbability in the belief that an accidental resemblance 

 to some common object was in each case the foundation for 

 the work of natural selection, since perfected through the 

 occasional preservation of slight variations which made the 



