MIMICRY AMOXGST THE BLATTID.E. 367 



opteryx, for there is visible a large curled-up spiral lying on the 

 dorsal face of the anterior part of the wing. But when the 

 wing is spread out it is seen that the method of wing-folding 

 is quite peculiar. The triangular apical area though large is 

 not sharply defined as in Chorisoneura, Theganopteryx, etc., and 

 the spiral fold involves not only this area but also the apical 

 portion of the anterior part of the wing, and a minute portion 

 of the apex of the posterior part. The part of the wing involved 

 in the spiral fold constitutes in fact a pseud-apical area, and it is 

 suffused with a dark fuscous colour, just as the true apical area of 

 Anaplecta and the apical triangle of Chorisoneura etc. are coloured 

 more deeply than the other parts of the wing. 



There can be little doubt that this type of wing- folding, unique 

 amongst the Blattidse, is a modification brought about by the 

 mimetic resemblance, and it is certainly a very singular one. 

 The student of the mimetic resemblances which exist between 

 insects not genetically related, frequently comes across remarkable 

 modifications of structure, modifications which are alien, so to 

 speak, to the constitution of the insects ; here a concentration of 

 pilosity to form a false spine, there a patch of colour, a shortening 

 of elytra, or a thickening of legs or antennae. But invariably he 

 will find these are modifications of structure absolutely essential 

 to the success and perfection of the mimicry ; if he looks deeper 

 he will find that mimicry has not touched parts which are 

 concealed, and which therefore play no part in the mimetic 

 resemblance. In short, mimicry is essentially a superficial likeness 

 between organisms fundamentally different. Yet here in the 

 species of Prosoplecta we have an exception to this very general 

 rule. The wing of the cockroach does not mimic the wing of the 

 beetle, but it has been modified because of the mimicry between 

 the two orders of insects, or in other words, in this case mimicry 

 has affected structures which play no part in a mimetic resem- 

 blance. To speak in the crudest of metaphors, it appears as if in 

 the production of these Coccinelliform cockroaches Nature had 

 been in a tremendous hurry. The immediate ancestors of 

 Prosoplecta were probably narrow and moderately elongate cock- 

 roaches with wings of the Ilemithi/rsocera type ; passage from 

 this form to a short convex form might have proceeded along at 

 least two lines — either the wings might have become gradually 

 shorter pari passu with the tegmina, as in certain species 

 of Ceratinoptera, Allacta, etc., or the wings could have been 

 adapted to an ovate, abbreviated body-form by passing through 

 a < horisonPMra~\\ke stage to the Anaplecta type. As a matter of 

 fact the evolution of Prosoplecta did not travel along either of 

 these lines,— the necessary shortening of the wing when in repose 

 has been produced by a rolling up of as much of the wing as was 

 necessary for the purpose, quite independently of the boundaries 

 between the intercalated apical triangle and the rest of the wing, 

 and so in defiance of the rule observed in all other species of the 

 family. 



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