10 Mr. H. Eltringham's Monograph of the 



material assistance in determining the sex of a specimen, 

 in the event of the abdomen and front-feet being missing, 

 as in a damaged example. In the great majority of 

 species the male claws are unequal, and thus if a single 

 leg remains, the sex can in those species be determined. 

 Probably in no genus is the question of sex more easily 

 decided. The female cloacal valves are very different in 

 appearance from the arched and hirsute tergite of the 

 male. Should this test fail the difference of structure 

 between the fore-feet of male and female is easily observed, 

 in many cases even with the unaided sight. Finally the 

 tarsal claws are, as stated, a certain guide in the majority 

 of species. In spite of these facts, which are by no means 

 new, many published works abound in errors as to the sex 

 of the species therein described, such errors adding greatly 

 to the difficulties of the systematist, more especially in 

 cases of unique types difficult of access. 



A phenomenon common to many Lepidoptera and 

 known as " seasonal dimorphism " is exhibited to a greater 

 or less extent by many species of Acraea, especially those 

 which mav be said to belong to the acrita and calditrena 

 groups. I do not propose on the present occasion to enter 

 upon a discussion of this interesting and complicated sub- 

 ject, which constitutes a special study in itself. It is, 

 however, necessary briefly to allude to the phenomenon as 

 manifested in this genus. 



^ . rt^o/wiis presents a dry-season male in which the spots 

 are exceedinglj^ small, and a female, the ground-colour of 

 which is yellowish brown. The corresponding wet forms 

 are a male, in which the black marks are all more highly 

 developed, and a female which is actually black, often 

 with a whitish subapical bar. Seventeen examples of 

 the species taken at the Victoria Falls in September are 

 all distinctly of the dry-season form. The only record I 

 have for that locality is 1906-7 when Sept. 1906 showed 

 barely "6 in., whilst in the previous May, June, July, and 

 August the fall was nil. The maximum occurred in 

 February 1907 when 14*7 in. of rain fell. Of five males 

 taken on the Lualaba R. in October, one is of the dry form, 

 one intermediate and two wet, whilst of five specimens 

 taken in May, four are wet and one intermediate. In this 

 region May, June, July, and August are the dry months 

 and March and November have the maximum rainfall, viz. 

 7"9 in. and 8"6 in. respectively, so that the specimens, having 



