352 
ZOOLOGICAL UTEIIATURE. 
micked ; (2nd) that in eight cases the mimickers are known to he 
very much scarcer than the species which they copy ; (3rd) that 
in five cases where the Danais or Acraa presents loeal forms, or 
merely slight varieties, even these are mimicked by individuals 
of the mimicking species ; (4th) that in three cases where the 
sexes of the insect mimicked differ remarkably from each other, 
the sexes of the rnimicker present corresponding differences ; and 
(5th) that in four cases observed by me in nature, it was next to 
impossible to distinguish the living rnimicker from the species 
which it imitated/^ 
John Watson has published (Mem. Lit. & Phil. Soc. Man- 
chester, iii. pp. 128-133, 259-269, pis. 1-3, 5-7) a series of very 
interesting and important observations on the plumules of 
Diurnal Lepidoptera, illustrated with very numerous figures by 
J. Sidebotham. These peculiar scales are confined to the 
males in various genera of Diurnal Lepidoptera, and vary greatly 
in structure. Watson suggests that they serve as air-vessels to 
give buoyancy to the insects. They vary much in number in 
different species, or even in difterent individuals of the same spe- 
cies. They are most easily detected on freshly captured insects. 
After remarking on the plumules of the Lyccenidce in his first 
paper, and on the difference between those of Lyccena and Da7iis, 
Watson adds : — 
“ The points desired to be insisted on as useful in this 
investigation are ; — 
“ 1 . That these plumules are always identical in different 
individuals of the same species, and therefore mere geographical 
or other varieties may be detected by this test; and that 
“ 2. In species nearly allied, so closely as to make them diffi- 
cult of distinction, these scales will be often found very di fferent, 
forming very certain and unquestionable divisions; while, on the 
other hand, speeies of easy separation in other physiological 
peculiarities have sometimes almost identical plumules.^^ 
In Watson^s second paper he remarks on the absence of 
plumules in all those species of PrioneriSy Papilio, Charaxes, and 
Gonepteryx which possess a serrated costa. The only species 
of Pieris on which Watson could detect no plumules were 
agathoriy protodicey and pallidicey although the closely allied 
daplidice and hellica possess them in abundance. The plumules 
of the P. lycimnia group somewhat resemble those of Euploca. 
AVatson suggests the term Idiolepides as more appropriate than 
plumules. They are generally found on the upper surfaces of 
the wings, sometimes most abundant on the primary, sometimes 
on the secondary, usually in or near the discoidal cells of both 
Avings ; but in the genus Euplcea they occur only in the upper 
part of the secondary wings, where overlapped by the primary, 
and fringing the light-coloured patch on the inferior wings ; 
here they exist in Euplcaa midanus in large and compact masses. 
