268 Mr, G. J. Arrow on Sexual DimmiJhism in 



any fundamental difference but in the degree of develop- 

 ment of the colouring matter, the male, with the excep- 

 tion of the aberrant individuals referred to of the Mexican 

 species, exhibiting a greater exuberance than the female, 

 or the superposition of a darker hue. Anomala im2')erialis, 

 described in this paper, is an apparent exception to this 

 rule, the colours of the two sexes appearing to be unrelated. 

 But experiment shows that the metallic purple colour 

 characteristic of the male of this species is transformed by 

 exposure to sunlight into a green like that of the female, 

 so that here also the male form is obtained by an addition 

 to that characteristic of the female. 



From this rule it results that, given a sufficiently wide 

 range of variation, the line of separation will be liable to 

 obliteration, and it may be found that certain individuals of 

 some of the species do not correspond with the sexual charac- 

 ters given; but this will not interfere with the general fact, 

 for in every case mentioned, (except that of Anomala cinna- 

 harina, where the original descriptions appear to warrant 

 my conclusion,) the number of specimens examined seems 

 sufficient to establish the general rule ; and several species 

 which in all probability belong to this category have been 

 omitted because the number of specimens I have been 

 able to examine is insufficient to be conclusive. 



It is important to notice, that the cases of aberration to 

 which I have referred are without exception of the female 

 sex, thus associating them with those cases familiar to us 

 amongst higher animals of the phenomenon of Gynandro- 

 morphism, which appears to be of occasional occurrence 

 wherever secondary sexual characters are found. 



Table of species exhibiting Sexual Dimorphism. 

 The Sexes differing in Claw Structure. 



Anomala egregia, Galian. 

 A. disparilis, sp. ii. 

 A. kersteni, Gerst. 



A. rufa, Kolbe . 

 A. solida, sp. n. . 

 A. clyjieata, sp. n. 

 A. transvalensi'i, sp 

 A. distanti, sp. n. 

 A. denuda, sp. n. 



Somaliland. 



Gold Coast. 



Zanzibar. 



Germ. E. Africa. 



S. Africa. 



S. Africa. 



Transvaal. 



Transvaal. 



Old Calabar. 



A. calcarata, sp. n. 



S. Africa, 



