IV] NEW-WORLD MIMICS 41 



in which, the pigment is retained. In Gastnia and in 

 Anthomysa the scales on the transparent parts which 

 are without pigment are also somewhat reduced in 

 size, being stumpier than the normal ones. At the 

 same time they tend to stand out at right angles 

 to the wing membrane^. The neck here again is 

 shorter in the transparent than in the pigmented 

 scales. A good deal of stress has been laid upon 

 this case by some supporters of the theory of mimicry, 

 since it is supposed to shew that a similar effect can 

 be brought about in a variety of ways ; consequently 

 the existence of this assembly of similar transparent 

 forms belonging to various families cannot be put 

 down as due to the effect of similar conditions, but 

 must be regarded as having arisen in each instance 

 in a different manner through the independent action 

 of natural selection ^. It is doubtful, however, whether 

 such a conclusion necessarily follows from the facts. 

 In all of the cases the process would appear to be 

 similar: loss of pigment, reduction in the size of the 

 scales, and eventually a tendency for the scales to 

 stand at right angles to the wing — ^this last part of 

 the process apparently depending upon the reduction 

 of the neck of the scale. It has been said that greater 

 transparency is brought about by the scales standing 

 out at right angles in this way, but as the scales them- 



^ This is more marked in Castnia than in Anthomysa. It appears 

 to be a peculiarity of many members of the geniis Gastnia that the 

 scales do not lie so tight as generally in moths. Owing to this, some 

 of the large whole-coloured species have a somewhat fluffy look. 



2 Cf. Poulton, Essays on Evolution, 1908, pp. 264-6. 



