INTKODUCTION. 



It must have been noticed by those lepidopterists who have read 

 the previous volumes of this work that I have repeatedly referred to 

 species as being " sexually dimorphic," in other words, that certain 

 sexes are to be readily distinguished by some characteristic trait which 

 is generally evident even on a superficial examination. Throughout 

 the animal kingdom, there are a large number of species, the sex of 

 which can be determined readily, apart from the sexual organs, by 

 some external structure or conformation which strikes the most casual 

 observer. On the other hand, there are species which have no outward 

 visible signs of their sex, which can be determined alone by the 

 special sexual organs with which most animals are provided. Lepi- 

 doptera are not behind-hand in this respect, and there are many 

 external characters by means of one or more of which the sexes may 

 be definitely distinguished without the examination of the sexual 

 organs. These external signs of sex have been termed " secondary 

 sexual characters." To these secondary sexual characters the term 

 " antigeny " is applied by Scudder, and comprises all " those accessory 

 peculiarities of either sex which are not directly connected with 

 generation." 



Of these characters in lepidoptera we find a large variety. In 

 fact, in some species or other almost any portion of the body may be 

 so modified as to become such, and thus we find the antennas, legs, 

 thoracic crests, abdominal crests, the wings as a whole, the nervures, 

 etc., all modified in particular species so as to become "secondary sexual 

 characters," whilst wing markings and colour are also in many instances 

 requisitioned for the purpose. 



Darwin in his " Descent of Man " has treated the subject of 

 " secondary sexual characters " very fully, and Geddes and Thompson 

 write : " Among invertebrates prominent secondary sexual characters 

 are rarely exhibited outside the great division of jointed-footed 

 animals or arthropods. There, however, among crustaceans and spiders, 

 but especially among insects, beautiful illustrations abound. Thus the 

 great claws of crabs are frequently much larger in the males ; and 

 male spiders often differ from their fiercely coy mates, in smaller size, 

 darker colours, and sometimes in the power of producing rasping 

 sounds. Among insects, the males are frequently distinguished by 

 brighter colours attractively displayed, by weapons utilised in dis- 

 posing of their rivals, and by the exclusive possession of the power of 

 noisy love-calling. Thus, as the Greek observed, the Cicadas "live 

 happy, having voiceless wives." Not a few male butterflies are pre- 

 eminently more beautiful than the females ; and many male beetles 

 fight savagely for the "possession of their mates " (' Evolution of sex,' 

 p. 6). Darwin argued that these " secondary sexual characters " 

 originated first of all in slight variations, that these variations were of 

 advantage in what he termed " sexual selection," a phrase adopted to 

 define the advantage due to actual selection, not by nature but by the 

 other sex, so that the individuals possessing advantageous variations 



