8o VARIATION IN EUROPEAN LEPIDOPTERA. ' 



in and often secures its transmittal either permanently or inter- 

 mittently through successive generations, especially if the peculiarity 

 be of advantage. And since aberrations are sometimes dependent 

 on sexual causes, we find that an insect occasionally develops two 

 distinct forms of one sex, while the other remains constant to type. 

 This is what is termed ' sexual dimorphism,' and is familiar to 

 English lepidopterists in the case of the female ab. Valezina of 

 Argy?ims Paphia. The normal female of A. Paphia is always of a 

 more sombre colouring than the male. The form Valezina is there- 

 fore nothing but an extreme development of this sexual tendency. 

 On the Continent this aberration crops up occasionally, but I doubt 

 if it is anywhere found in any degree of abundance except in the New 

 Forest in England. The genus Colias presents instances of female 

 dimorphism. The following species have occasional female forms of 

 bleached coloration : — C. Edusa ab. Melice, C. Palceno ab. Lappofiica, C. 

 E?'ate2ih. Pallida. I will not, however, weary you with names, but refer 

 to the remarkable case of this sexual tendency presented by the exotic 

 Papilio Memnon, as described by Wallace. The females of this insect 

 vary greatly, but may be divided into two groups — namely, those which 

 resemble the male in shape, and those which differ entirely from him 

 in having developed a large spoon-shaped tail on the hind wing, of 

 which no rudiment is visible in the ordinary type of either sex, 

 and in being also characterised by a distinct colour. That they 

 are all the offspring of the same form has been proved by their 

 having been all three bred from the same batch of eggs. The females 

 of several exotic Papilionidae develope similar phenomena under the 

 influence of mimicry, but I have not time to refer to examples. 

 Before I pass from the subject, I may remark that Darwin ('Origin of 

 Species,' ch. v., p. 150), speaking of secondary sexual characters, 

 remarks that these are more rarely found in the female than in the male, 

 which rule however, I do not think holds good in the order 

 Lepidoptera as in other fields of zoology. 



But the phenomenon of Dimorphism occurs quite independently 

 of sex. Species occasionally throw off aberrations presenting peculiar 

 characteristics which recur from time to time. Such dimorphic 

 forms are to be met with in Tephrosia Biundularia an*d T. Crepiiscu- 

 laria, I mean the dark melanic variety with a pale marginal scalloped 

 line. The history of this variety, (for it has now become established) 

 we owe to the industry of Mr. Llewellyn, of Swansea, who has given 

 a detailed description of the experimental breeding of this form in 

 the Entomologists' Mo?ithly Magazine^ vol. xvii. By mating a male 

 and female of this aberration, and continuing the process for five 

 years, he at length succeeded in breeding ninety-seven specimens 



Naturalist, 



