( clxxv ) 



that purpose are such as are common to both sexes (colour, 

 pilosity, puncturation, etc.). Again, in many species of 

 Anthophora, Eucera, etc., the middle legs of the $ $ differ 

 extraordinarily from those of their females ; but in other 

 ^ $, and in all the $ $, the characters of the middle legs are 

 in no way remarkable, and are seldom, if ever, employed to 

 distinguish one species from another. 



I do not mention these apparent exceptions to Darwin's 

 rules with any idea of questioning the general applicability 

 of the rules themselves to the Animal Kingdom as a whole. 

 But it certainly seems to me, that the case of the characters 

 now under consideration presents a remarkable exception to 

 them, and one which I ought not to leave unnoticed. 



I have now to attempt such a description as the time at 

 our disposal will permit, of the phenomena — or rather of some 

 of the phenomena — summarised in the above generalisations. 

 Merely for the sake of convenience I shall divide them rovighly 

 into Structural and Coloration-characters, and subdivide the 

 latter according as they appear in the integument, or the 

 pilosity, or elsewhere ; but I do not attach importance to this 

 classification, for Colour is really dependent in many cases 

 on facts of Structure, and even where actual pigment is 

 present (which is not always the case) the colour-effect 

 produced does not always entirely depend upon it. 



However, commencing with characters independent of colour, 

 such as would generally be reckoned as Structural in the 

 strictest sense of the word, let us take, first, one which 

 runs throughout the whole group, and, in fact, appears to 

 have originated before the separation of the Hymenoptera 

 from other Arthi-opodous animals, — the greater size of the 

 Female. 



Female Aculeates are almost always larger than their males, 

 but (except in some Ants) hardly paradoxically so. In fact, 

 in many genei'a the difference is slight, and hardly to be 

 appreciated except in long series of both sexes. 



This general rule has become well known, because it had 

 the good fortune to attract the notice of Darwin, to whom 

 it was communicated (as he tells us) by Frederick Smith. 

 He cites (also on Smith's authority) four cases of exceptions 



PROC. ENT. see. LOND., V. 1912, M 



