( clxx ) 



shall ask leave to use the term in a somewhat narrower sense, 

 excluding (1) all concealed or internal characters, i.e. such as 

 cannot be examined without dissection of specimens, and 

 (2) characters which, though " attached to one sex " — in the 

 sense that, in a particular species or group of species, one 

 sex only exhibits them — seem clearly not to have been 

 developed independently in it as an adaptation to its special 

 bionomy, but to have come to it by Inheritance simply — 

 as may be inferred from the possession of like charactei's 

 by most other organisms of the same ancestry whatever be 

 their surroundings and habits. Thus, inasmuch as Insects 

 of all kinds and both sexes normally possess wings and 

 ocelli, I shall not treat as a sexual character the presence of 

 these structures in a c? Insect whose 9 lacks them. To take 

 an actual instance of this — Mutilla europaea $ has wings 

 and ocelli, not because it is a male — not, therefore, as a 

 character arising out of its sex, but simply because it is a 

 normal Insect. Contrariwise, the absence of wings and 

 ocelli in the 5 of the same species is strictly a sexual 

 character, an actual modification and alteration of the 

 structures normally inherited in the group to which it 

 belongs, and one which we have reason to think is adapted to 

 the habits of that particular sex in that particular species. 

 On the other hand, a spur-like appendage which is attached 

 to the hind femur in. ^ $ only of Panurgus calcaratus (a 

 Bee), Avhich is not normally characteristic either of the Class 

 or the Order or the Family or the Genus including that species, 

 and which may be reasonably thought to serve a useful 

 purpose in that sex exclusively of that particular insect — this 

 and similar structures, attached to one sex only and demon- 

 strably not merely inherited by it, may be set down without 

 hesitation as simply and solely sexual characters. I do not 

 think that this is a " distinction without a difference," but 

 one always to be borne in mind in reasoning on the significance 

 of characters in which the sexes differ. Such characters may 

 be in any particular case either sexual in their origin, or 

 sexual only in the sense that they are in fact limited to one 

 sex because the other sex has lost them. 



i\mong Aculeate Hymenoptera some of the best modern 



