156 Dr. F. A. Dixey on 



females." * This dulness of coloration iii the wet-season 

 females mentioned is with some hesitation interpreted by 

 Mr. Marshall as being protective in its object. The present 

 is perhaps a fitting opportunity for pointing out that the case 

 of these three Acnvas seems to bear some relation to a far- 

 reaching principle which has met with less notice than it 

 deserves, and as to the significance of which no suggestion 

 has hitherto been made. The principle I refer to is 

 this : — that the dry-season garb of a seasonally dimorphic 

 butterfly, at least as regards its under-suiface, is often far 

 better marked and more persistent in the female than in 

 the male. This is obviously of interest in view of Professor 

 Poulton's interpretation of the cryptic character of dry- 

 season and desert forms."|* It would accord with all that 

 we know as to the special importance attaching to the 

 life of the female, and the means that are taken for 

 preserving it, that the more efficient mode of protection, 

 such as on Professor Poulton's hypothesis the dry-season 

 colouring must be, should be more completely and persist- 

 ently adopted by the sex whose safety from enemies is of 

 such vital moment to the species. The interest of the 

 point perhaps justifies a slight digression, and I propose to 

 give here a few instances which will serve to support the 

 above generalization, 



Xanthidia niciirpc, Cram. North and Central America. 

 The wet-season female retains on the under-surface a 

 tinge of the dry-season purple. 



Ixias pyrcnc, Linn. India, etc. Here also the wet- 

 season female usually retains the dry-season mottling. 



I'xias marianm, Cram. India. The wet-season female 

 is nearly always brown beneath, as are both sexes in the 

 dry season. The under-side of the wet-season male is 

 yellow. 



Cato2JsUia ijoriiona, Fabr. Oriental and Australian 

 Region. In the wet-season form {G. crocale, Cram.):J: the 

 female often retains in some degree the dry-season 



* Tiaus. Ent. Soc, Lond., 1902, pp. 433, 434. It is hardly nee-es- 

 sary to remark that the peculiar need for protection experienced by 

 the female sex was lirst pointed out Ijy Mr. Wallace. Some of the 

 provisions towai'ds this end were recognized by him as cryptic (as 

 in many birds) ; others were supposed to be pseudaposematic. It 

 is now known that synaposematism may also play an important part 

 in the special protection enjoyed by female insects. See Trans. Ent. 

 Soc. Loud., 1902, pp. 46(j, 467, ibique cit. 



t Ibid., pp. 431-433, etc. t Ibid., p. 109. 



