202 MISCELLANEOUS OBJECTIONS TO THE 



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 color, 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 oscillation, of infinitesimal beginnings 

 can ever build up a sufficiently 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 resem- 

 blance to an object commonly found in the stations fre- 

 quented by them. Nor is this at all improbable, consider- 

 ing the almost infinite number of surrounding objects and 

 the diversity in form and color 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) resemble for the sake of protection special objects, but 

 only the surface which commonly surrounds them, and this 

 chiefly in color. Assuming that an insect originally hap- 

 pened to resemble in some degree a dead twig or a decayed 

 leaf, and that it varied slightly in many ways, then all the 

 variations which rendered the insect at all more like any 

 such object, and thus favored its escape, would be preserved, 

 while other variations would be neglected and ultimately 

 lost ; or, if they rendered the insect at all less like the 

 imitated object, they would be eliminated. There would 

 indeed be force in Mr. Mivart's objection, if we were to 

 attempt to account for the above resemblances, independ- 

 ently of natural selection, through mere fluctuating varia- 

 bility ; but as the case stands there is none. 



Nor can I see any force in Mr. Mivart's difficulty with 

 respect to " the last touches of perfection in the mimicry ; " 

 as in the case given by Mr. Wallace, of a walking-stick in- 



