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V. Seasonal Dimorphism in African Butterflies. By 

 ARTHUR G. BUTLER, Ph.D., F.L.S., etc. 



[Read February 3rd, 1896.] 



MR. GUY A. K. MARSHALL'S "Notes on Seasonal 

 Dimorphism in South African Rhopalocera" (Trans. Ent. 

 Soc. Lond., 1896, p. 551), as observed by him in 

 Mashunaland, are of great interest and form a contribu- 

 tion to science which will be very useful to future workers, 

 as exhibiting a part of the truth relating to this engross- 

 ing subjec f ; but a part only, as it is now my object to show. 



Mr. Marshall has evidently misunderstood my remarks 

 respecting seasonal and local modifications of species ; 

 he has indeed wholly missed my point, which is this : 

 in a country which is hot and dry throughout the year 

 wet-season forms will be naturally extremely rare (if 

 present at all), whereas the reverse will be the case in an 

 uniformly moist climate. Now where a species ranges 

 throughout Africa to Arabia, it exhibits in one locality 

 a single type (say dry-season), arid perhaps in abnormal 

 seasons when light showers fall, a second type (inter- 

 mediate between dry and wet) ; or if the country be 

 moist a wet-season and an intermediate-season form 

 occur, but no dry-season form. Such is frequently the 

 case in Sierra Leone. 



In countries where the wet season is out of all propor- 

 tion to the dry, the wet-season form of a species will be 

 naturally better marked ; and the reverse will hold good 

 where the dry season has the advantage. 



It is very likely that Mr. Marshall may be correct in 

 his opinion, based upon practical experience in Mashuna- 

 land, that, in Acrtea, I have called the dry-season form 

 " wet/' and the wet-season form " dry/'* but I am 



C: " He however makes an exception in the case of A. bomba (= 

 induna). 



TRANS. ENT. SOC. LOND. 1897. PART T. (APRIL.) 



