(i, ERY =) 
noted by Mr. Marshall to become dominant about the middle 
of March. 
“ Larvee previously captured also produced sesamus at this 
period, whereas an exactly similar individual that had been 
placed ina 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.,’ /.c.) ; 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 seswmus 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 chanee 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 | 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 8. Africa, 
it might appear that the mimetic form would be found at the time 
of greater stress, viz. the dry winter season. But in England, 
although there are abundant examples of insects with warning 
colouring and many which mimic them in the summer, when there 
isa plentiful supply of palatable food, in winter none are to be 
