II.] INCIPIENT STRUCTURES. 41 



these creatures obtained by myself in Borneo {Ccroxylios 

 laceratus) was covered over with foliaceous excrescences 

 of a clear olive-green colour, so as exactly to resemble a 

 stick grown over by a creeping moss or jungermannia. 

 The Dvak who broudit it me assured me it was grown 

 over with moss although alive, and it was only after a most 

 minute examination that I could convince myself it was not 

 so." Again, as to the leaf butterfly, he says:^ "AVe come to 

 a still more extraordinary part of the imitation, for we find 

 representations of leaves in every stage of decay, variously 

 blotched, and mildewed, and pierced with holes, and in 

 many cases irregularly covered with powdery black dots, 

 gathered into patches and spots, so closely resembling the 

 various kinds of minute fungi that grow on dead leaves, 

 that it is impossible to avoid thinking at first sight that 

 the butterflies themselves have been attacked by real 

 fungi." * 



Here imitation has attained a development which seems 

 utterly beyond the power of the mere " survival of the 

 fittest "to produce. How^ this double mimicry can impor- 

 tantly aid in the struggle for life see.ms puzzling indeed, 

 but mucli more so how the first faint beoinnino-s of the 

 imitation of such injuries in the leaf can be developed in 

 the animal into such a complete representation of them — 

 a fortiori how simultaneous and similar first beginnings of 

 imitations of sucli injuries could ever have been developed 

 in several individuals, out of utterly indifferent and inde- 

 terminate minute variations in all conceivable directions. 



Another instance which may be cited is the asymmetrical 

 condition of the heads of the flat-fishes (Pleuronectidit), 

 such as the sole, the flounder, tlie brill, the turbot, &c. In 



1 Loc. cit. p. 60. 



