444. Mr. G. A. K. Marshall on 



In a normal wet season (in which there are more or less 

 continuous heavy rains from the middle of December to 

 the end of February) P. sesamus appears at the end of 

 March. Last season we had heavy rains up to the end of 

 December 1897, but January was unusually dry and 

 sesamus appeared on Feb. 6, being the earliest record I 

 had for it. Tliis season the drought was still more severe 

 in January and commenced earlier, viz. about Dec. 12. 

 This has been accompanied by a still earlier appearance of 

 sesamus 0. The evidence so far as it goes tends to show 

 that climatic conditions, in some cases at least, are directly 

 capable of inducing the change and upsetting the normal 

 alternation of the forms. Here, owing to highly abnormal 

 conditions, we have the dry form occurring at what is 

 normally the very lieight of the wet season. Moreover, 

 ever since I have observed seasonal dimorphism in butter- 

 flies I have noticed the effect of abnormal weather in 

 retarding or accelerating the appearance of either form, 

 and Barker has made similar observations at Malvern, near 

 Durban, Natal." 



" Salishuri/, April 25, 1899. — The sesamus form is 

 evidently more dominant than the natalensis, for despite 

 the heavy rains in February 1899 the latter made very 

 little headway after the appearance of the dry-season 

 form ; whereas among such insects as the Pierinie the 

 result of the alternating extremes was much more 

 evident." 



''Salisbury, Fch. 7, 1900. — In spite of our heavy rains 

 during January (16 75 inclies for the month) the winter 

 forms of Precis are appearing just as early as last year, 

 which has puzzled me considerably. I shall send you the 

 first examples of each form captured." 



" Salislmrif, June 20, 1900. — I am afraid I am not yet 

 convinced as to the automatic alternations [viz. due to the 

 organism itself and not to external stimuli] of the seasonal 

 forms in P. sesamus ; there seems to be at present an equal 

 amount of evidence on either side, and until the matter 

 can be settled by an exhaustive series of experiments I 

 must retain an open mind on the question." 



I have given below a list of all the specimens of the two 

 phases of Precis sesamus sent to me from Mashonaland by 

 Mr. Marshall. 



