Chap. TO.] THEORY OF NATURAL SELECTION". 283 



We will return to Mr. Mivart's other objections. In- 

 sects often resemble for the sake of protection various 

 objects, such as green or decayed leaves, dead twigs, 

 bits of lichen, flowers, spines, excrement of birds, and 

 living insects ; but to this latter point I shall hereafter 

 recur. The resemblance is often wonderfully close, and 

 is not confined to colour, but extends to form, and even 

 to the manner in which the insects hold themselves. 

 The caterpillars which project motionless like dead twigs 

 from the bushes on which they feed, offer an excellent 

 instance of a resemblance of this kind. The cases of 

 the imitation of such objects as the excrement of birds, 

 are rare and exceptional. On this head, Mr. Mivart 

 remarks, " As, according to Mr. Darwin's theory, there 

 is a constant tendency to indefinite variation, and as 

 the minute incipient variations will be in all directions, 

 they must tend to neutralize each other, and at first to 

 form such unstable modifications that it is difficult, if 

 not impossible, to see how such indefinite oscillations 

 of infinitesimal beginnings can ever build up a suffi- 

 ciently appreciable resemblance to a leaf, bamboo, or 

 other object, for Natural Selection to seize upon and 

 perpetuate." 



But in all the foregoing cases the insects in their 

 original state no doubt presented some rude and 

 accidental resemblance to an object commonly found 

 in the stations frequented by them. Nor is this at all 

 improbable, considering the almost infinite number of 

 surrounding objects and the diversity in form and colour 

 of the hosts of insects which exist. As some rude 

 resemblance is necessary for the first start, we can 

 understand how it is that the larger and higher animals 

 do not (with the exception, as far as I know, of one fish) 



