II.] INCIPIENT STRUCTURES. 49 



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. fit- 

 test " to produce. How this double mimicry can impor- 

 tantly aid in the struggle for life seems puzzling indeed, 

 but much more so how the first faint beginnings of the im- 

 itation of such injuries in the leaf can be developed in the 

 animal into such a complete representation of them a for- 

 tiori how simultaneous and similar first beginnings of imi- 

 tations of such injuries could ever have been developed in 

 several individuals, out of utterly indifferent and indetermi- 

 nate infinitesimal variations in all conceivable directions. 



Another instance which may be cited is the asymmetrical 

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

 such as the sole, the flounder, the brill, the turbot, etc. In 



PLETJBONECTID.E, WITH THE PECULIARLY-PLACED EYE IN DIFFERENT POSITIONS. 



{From Dr. Traquair's paper in the " Transactions of the Linnean Society, 1865.'') 



all these fishes the two eyes, which in the young are situ- 

 ated as usual one on each side, come to be placed, in the 



adult, both on the same side of the head. If this condi- 

 3 



