EXTERNAL ANATOMY OF INSECTS. 645 
face, as in the great majority entirely to conceal that 
substance. Whether these are really most analogous to 
plumes or scales has been thought doubtful. De Geer 
is inclined to think, from their terminating at their 
lower end in little quills, and other circumstances, that 
they resemble feathers as much as scales*; Reaumur on 
the contrary suspects that they come nearer to scales *. 
Their substance, approaching to membrane, seems to 
make further for the former opinion, and their shape and 
the indentations that often occur in their extremity, fur- 
nish an additional argument for the latter. Their num- 
bers are infinite; Leeuwenhoek found more than 400,000 
on the wings of the silk-worm moth (Bombyx Mori) °¢ ; 
and in those of some of the larger moths and butterflies 
the number must greatly exceed this. You will observe 
however that in many Lepidoptera the wings are partially, 
and in some instances generally, transparent: thus in 
Uria Proteus, a butterfly before noticed for the long tail 
that distinguishes its secondary wings, there are many 
transparent spots; in Attacus Atlas, one of the largest 
of moths, and its affinities, there is as it were a window 
in each wing formed by a transparent triangular space ; 
in A. Polyphemus, Paphia, &c., the pupil of the ocellus is 
transparent, which in the former is divided by a ner- 
vure. In several of the Heliconian butterflies, and in 
eygena, &c., the greater part of both wings is trans- 
parent, with scales only upon their nervures, round their 
margin, or forming certain bands or spots upon them ; 
in Parnassius Apollo, Mnemosyne, &c., the scales are so 
arranged as not wholly to cover the wings, which renders 
them semidiaphanous.; and in some (Nudaria) the wings 
4 De Geer i. 63—. > Reaum. i. 200. 
© Hoole’s Leeuwenhoek, i. 63—. 
