LEPIDOPTERA. 315 
species, especially Saturnia pavonia major, I have found this piece to 
be of a similar consistence with the other abdominal segments. 
The wings are attached to the lateral and superior parts of the 
meso- and meta-thorax, and are always present, except in a few species, 
of which the females alone are apterous, or have the wings reduced to 
small and useless appendages : these wings are of large size, and are not 
folded up * ; the two fine layers of membrane of which the wings are 
composed, like the upper and lower surface of a leaf, are kept expanded 
by a number of longitudinal corneous veins, or nerves, as they have 
been called, but which Dr. Leach termed Pterygostia, or wing-bones. 
These veins here as in the Diptera and Hymenoptera, according to their 
number and position, offer very important characters for generic dis- 
tribution, but which have been too much neglected by Lepidopterists. 
M. Boisduval, in his recent work, has delineated these nerves in many 
of the genera of butterflies; although it is but proper to observe in 
justice to our own countrymen Harris and Jones, that they long 
ago published observations on this subject, the latter in the 2d vol. 
of the Linnean Transactions, in which the same subject was well 
treated. The wings in this order offer another peculiarity, since, 
instead of being naked and transparent, they are clothed with 
a double layer of minute scales, somewhat resembling those of 
fishes. ‘These scales, upon which the beauty of these insects so 
entirely depends, are easily detached in the form of a fine dust, and, 
when examined under the microscope, are exceedingly variable in 
their form, but generally more or less wedge-shaped, or oval ; some- 
times toothed or notched at the broadest end, and having a slender 
point at the base, by which they are attached upon the membranous 
surface of the wing, which, when denuded, presents the appearance of 
numerous minute impressions arranged in lines, in which the base of the 
scales are planted, being laid upon each other like the tiles on the roof 
of a house (_fig.105. 5.). Lyonnet, in his posthumous memoirs, has filled 
several quarto plates with representations of these scales, varying to 
almost every form, taken from the wings and body of the goat moth, 
so that the suggestion of a writer (Mag. Nat. Hist. No. 11.), that the 
form of these scales might be used for specific characters, is entitled 
tono weight. Some species have a double layer of these scales on both 
sides of the wings, the under layer usually consisting of white scales. 
The number of these scales is very great, there being more than 
* The Pterophori offer a partial exception to this rule. 
