The Bionomics of South African InsccU. 415 



differences in the insect life of the two seasons, will all be 

 shown to be consistent with the above hypothesis. 



Tlie results of Mr. Marshall's experiments as to the 

 nature ol" the stinnilus by which the change is started in 

 any individual will be discussed, and further lines of 

 investigation suggested. The much greater size and 

 weight of the dry phases will be shown to have an import- 

 ant bearing upon the inquiry, indicating, as it does, that 

 the phase must be predetermined in the larval stage. 



Finally, it will be argued that the facts proved by Mr. 

 Marshall, although most startling and indeed astounding, 

 are not subversive of any of the principles of the science 

 of systematics. 



B. Historical. 



In his great work on " South African Butterflies " 

 (London, 1887, vol. i), Mr. Roland Trimen describes several 

 intermediate varieties between Precis natalensis and F. scsa- 

 mus, and records Mr. F. N. Streatfeild's capture of the two 

 hutter^ies in coitu. He concludes (/oc. a/, pp. 231 and 233), 

 " It is only to such occasional unions, and to their fertility, 

 that the origin of the intermediate examples under notice 

 can be attributed." 



Mr. Trimen also makes a similar suggestion as to the 

 intermediate varieties between ^yclasgis and archesia, which 

 are also recorded as having been taken in coitu Qoc. cit. p. 

 235). 



Mr. Guy A. K. Marshall first published in 1896 the 

 suggestion that a group of South African butterflies 

 described and known as different species of the genus 

 Precis or Junonict were in reality the seasonal phases of a 

 comparatively limited number of species. He pointed 

 out, however, that octavia and amcstris (s. /.) had been 

 previously considered as two forms of a single species by 

 M. Charles Oberthiir of Rennes (Ann. Mus. Genov. xviii, 

 1883, p. 721), and also that Mr. C. N. Barker, the distin- 

 guished Natal naturalist, had been long convinced of the 

 existence of these seasonal phases, and especially of the 

 most remarkable case of all, P. sesamus, and its wet-season 

 form, natalensis. 



Mr. Marshall's general description of the differences be- 

 tween the two phases is as follows : " The dry-season form 

 is smaller, and usually assumes a duller type of colouring 

 on the upper-side, sometimes of quite a different hue; the 



