522 Dr. A. G. Butler on Seasonal Dimorphism. 



practically from the same cause, and in some cases it 

 will be very hard to draw the line between them : a 

 uniformly moist locality may produce only a wet-season 

 form, and a dry locality the converse ; yet one could 

 hardly speak of Acrsea pseudegina as a seasonal form of 

 A. natalica, but merely as a western development of 

 that species (an intermediate form completely linking 

 the two extremes occurs in Angola) . 



Whether the colour variations of Acrssa johnstoni and 

 other members of the A. esebria group are seasonal 

 seems doubtful ; indeed, from the evidence before me, I 

 should say certainly not ; for we have extreme forms, 

 collected within three days, that is to say, with only one 

 day's interval between, and, moreover, both forms are 

 in admirable condition. The species of the A. esebria 

 group are therefore probably simply inconstant, no 

 satisfactory reason for such inconstancy being at present 

 known, or even guessed at. 



The above observations will, I hope, help to impress 

 upon collectors the importance of noting not only dates 

 of capture of every specimen which they obtain, but also 

 the altitude and nature of climate, so that Lepidopterists 

 may have some definite data to work from in deciding 

 these interesting questions touching the climatic re- 

 lationships or seasonal dimorphism of the insects which 

 come into their hands. 



