448 Mr. G. A. K. Marshall on 



The succession of the seasons is very different, in the 

 region in which Mr. and Mrs. Hindc captured the butter- 

 flies, from that which obtains in Salisbury. The two 

 forms of succession are shown in parallel columns below. 



british east africa mashonaland 



(machakos, kitui, etc.). (SALI.SBURY, mazoe, gadzima). 



Mid-Octolier ^ Small wet season | Early Nov«ml)er ^ Wet season, aver- 

 to - (about 17 — 18 I age rainfall of 

 Mid-December ' inches). \ to j Salisbury about 



*o > Small dry season, 



Mid-Marcli i „. ^ 



^ ~\ liig wet season 



end May / (•'^^°"\ l^-^'^ 



•^ ^ inches). 



Mid-October | Big dry season. 



■ Dry season. 



It is to be observed that the rainfall of the small and 

 the big wet seasons are about the same, and also that the 

 country is not really dried up in the small dry season 

 except in unusually dry years. The country is always 

 dried up in the big dry season. 



In spite of these great differences in the seasons, the 

 succession of the phases is wonderfully alike in the two 

 areas, as has been pointed out above. We nuist conclude 

 that semmus can produce two seasonal phases annually 

 but not more, so that the small dry season of the north 

 is no more effective in producing the dry phase than the 

 simultaneous wet season of the south. The species is so 

 constituted that it produces a dry phase for the big dry 

 season and a wet phase for the rest of the year, some of 

 the dry-phase individuals being produced some months 

 before the normal change takes place, viz. at and just 

 before the beginning of tiie chief dry season. The differ- 

 ence between the date at which this great change of 

 seasons takes place in north and south is attended by a 

 corresponding difference in the date at which the wet 

 phase of scsanvvs gives place to the dry. Both lists are 

 unfortunately wanting at the transition from the big dry 

 season to the wet. There is indeed only a single record 

 for the period between the beginning of June and the 

 beginning of December. Speaking from memory, Mr. 

 Marshall thinks that the break from sesamus to natalcnsis 



