504 Mr. G. A. K. Marshall on 



and would be quite sufficient to deter the bird from 

 attempting to eat butterflies of that colour. This is from 

 a mathematical point of view solely, but, from what I 

 know of these two forms in life, I believe that presuming 

 them to occur in equal numbers, a larger proportion of 

 echcria would actually be captured, for mima is a much 

 more shy insect, and although it has the same slow sailing 

 flight (when undisturbed) it does not keep on the wing 

 nearly as long as echcria; moreover, it is much more wary 

 and always on the alert for danger, going off at a smart 

 pace when frightened, and not returning to the same spot 

 as echeria frequently does after being struck at ; altogether 

 it is a much more difficult insect to capture. Indeed I 

 do not see why the mimic should not even somewhat sur- 

 pass the mimicked species in numbers, without upsetting 

 their relations to one another, jDrovided the taste of the 

 latter be sufficiently unpleasant, and particularly if the 

 flavour be of a lasting nature." 



"Malvern, Ma-y 14, 1897. — I feel quite satisfied that 

 Pscudacr^a trimenii is a mimetic and not a protected 

 species. In spite of its larger size it looks wonderfully 

 like AcTc'^a acara on the wing, and the first few examples 

 I caught completely took me in. Their flight is like that 

 of all Pseudacroeas and Euralias — slow and sailing — so 

 long as they are not disturbed ; but if struck at and missed 

 they are off like a shot and do not often give one a second 

 chance. At this particular spot (Malvern) they are a good 

 deal commoner than A. acara, which is only a rare visitor. 

 The latter is however common on the immediate coast, 

 where P. trimenii is I am told prett}^ plentiful in good 

 seasons." 



" Salish'ury, Jan. 12, 1901. — I quite agree with you that 

 the resemblance between the under-sides of Delias jmnclcmia 

 and Ishco'ta. pande^nia is the most remarkable case yet 

 brought forward, and one cannot but marvel how such 

 exact similarity can have been arrived at. Although I 

 should certainly incline to the belief that the mimicry is 

 Miillerian, judging by the congeners of both forms, yet its 

 very exactitude seems to be a difficulty, for although one 

 can readily understand how in an edible and much- 

 persecuted species the resemblance might be brought up 

 to so high a grade, yet it is hard to understand how this 

 could be effected in a species which is comparatively 

 immune from attack. For it seems to be an inevitable 



