The red form (nakdensis) was captured on Feb. 13, 1898, 

 (a pair in coitu) and Feb. 20, the blue form (sesamus), on 

 March 2, 12 and 16, and April 2. The latter form was 

 noted by Mr. Marshall to become dominant about the middle 

 of March. 



" Larvae previously captured also produced sesamus at this 

 period, whereas an exactly similar individual that had been 

 placed in a damp jar on March 23 and pupated April 1, 

 produced on April 13 the typical natalensis now exhibited. 

 It would be of the utmost value to have many more ex- 

 periments of the kind. 



" Of far greater importance is the fact that Mr. Marshall 

 has succeeded in breeding sesamus from natalensis in three 

 cases (' Ann. and Mag. Nat. Hist.,' I.e.) ; two are exhibited, 

 the third is in the British Museum. Of the former, one 

 parent laid three eggs on Feb, 27, of which two produced 

 butterflies, one a typical sesamus (larva, March 5-31 ; pupa 

 March 31 to April 15), the other a red natalensis tending 

 slightly towards sesamus in its heavy black markings and 

 blue-marked border (larva March 5 to April 5 ; pupa 

 April 5-20). The second parent laid one egg on March 6 

 which produced a typical sesamus (larva March 12 to April 7 ; 

 pupa April 7 — 30). This larva was placed in a damp jar 

 from March 30 to April 5, but the ' dry form ' of imago 

 emerged. The third example, in the British Museum, is a 

 sesamus bred from an egg laid by the summer form on Feb. 

 13 (larva, Feb. 19 to March 20 ; pupa, March 20 to April 4). 



" As to the meaning of this seasonal dimorphism, I agree 

 with Mr. Marshall's suggestion that the red natalensis, 

 appearing as it does in the keener struggle ' of the warm 



1 Mr. Blandford has pointed out, and the objection occurred to me 

 independently, that the press of life in the warm damp summer may 

 not, and probably does not, mean greater chance of destruction for 

 any individual insect, the larger needs of enemies being more than 

 compensated for by an increased supply of food. The question can- 

 probably be decided on the spot, and I am writing to Mr. Marshall 

 on the subject. In this climate the argument certainly holds good, 

 the danger to individuals of the comparatively few winter species 

 being probably far greater than to those of the numerous summer 

 forms. Granted that somewhat similar conditions exist in S. Africa, 

 it might appear that the mimetic form would be found at the time 



