NATURAL SELECTION SINCE DARWIN 87 



mentioned as illustrating perfect mimicry, the re- 

 semblance to a leaf is even more extraordinary. At 

 rest and with folded wings, this butterfly reproduces 

 in every detail the dry leaves among which it lives. 

 The real ribs of its wings, its head, and its body are 

 almost invisible; the ribs of the leaf it imitates are, on 

 the contrary, very clearly drawn. The resemblance 

 does not end there; it goes so far as to show almost 

 affectation. The wings frequently bear reddish or 

 yellowish flecks imitating fungous spots, and are in 

 places transparent and scaleless, thus reproducing ex- 

 actly the perforations of a leaf by worms or insects. 

 These precautions appear almost exaggerated and it 

 is very probable that in our description we substitute 

 our own visual impressions for those which this but- 

 terfly produces on its enemies. A rough general 

 likeness as to colouring or shape would undoubtedly 

 suffice to enable the butterfly to remain unnoticed 

 among the leaves. 



We could make the same remark about other cases 

 of exaggerated development such as the tusks of the 

 Babirussa (a boar of the Malay Islands), which, be- 

 ing rolled spirally can no longer be used for fighting. l*~ 

 For these facts, some explanation must be found other 

 than natural selection. 



In the arguments which we have presented, the dif- 

 ferent variations were considered as isolated, as in- 

 dependent, so to speak, from the rest of the organ- 



