i6 NATURAL SCIENCE. ^t^™' 



is by no means always correct ; and the existence of such forms 

 is a difficulty in the way of accepting the theory of mimicry. If a 

 butterfly has abandoned the usual dress of its genus without any 

 object in doing so, it might fairly be asked whether, when a resem- 

 blance to another form does occur, it is not accidental. If a diver- 

 gence from the normal style of colour and marking does not always 

 go with the existence of a prototype belonging to a different genus 

 or family, a certain amount of doubt is naturally thrown upon the 

 validity of the explanation in other cases where there is a prototype. 

 Mr. Scudder has suggested this difficulty, and has grappled with it 

 in his magnificent work upon the butterflies of North America, 

 recently published.'^ He quotes two suggestions that have been 

 made by way of explaining the matter. The first is the obvious one 

 that the model which is imitated does exist, but has not been found ; 

 the second suggestion is that the prototype did exist, i.e., that it 

 has become extinct. The mimicking form may then be supposed 

 to have secured and established its position by the help of its 

 vanished model, just as a dishonourable firm may trade for a time 

 under an old-established name no longer represented in the firm. Both 

 these suggestions are easier to make than either to prove or refute. 

 The third explanation is the most satisfactory. Mr. Scudder believes 

 that in cases of this kind we have to do with a general mimicry in 

 course of conversion into a special mimicry — that is to say, the 

 mimicking insect has got so far as to bear a certain likeness to the 

 members of another group, but has not yet acquired a particular 

 likeness to any one species. The general resemblance might in the 

 meantime profit the insect. The Marbled White butterfly may be 

 mentioned as a possible example ; it has departed from the usual 

 brown colour of its immediate relatives, and has become something 

 like the " Whites," but is not yet like any one species. A compara- 

 tively small change would convert it into a good likeness of any 

 species of " White." 



Frank E. Beddard. 



" Butterflies of the Eastern United States. 



