EXTERNAL ANATOMY OF INSECTS. 647, 
instances this is in transverse lines, which sometimes 
vary a little from a rectilinear course, and the extremity 
of the scales of one row reposes on the base of those of 
the succeeding one, so that in this respect their arrange- 
ment is like that of tiles in a roof: in some cases it is 
not so regular: thus the minute scales on the wings of 
Parnassius Apollo, and others with subdiaphanous wings, 
are arranged without order ; in Pontia and other Diurnal 
Lepidoptera, and many of the Crepuscular and Noctur- 
nal, there appears to be a double layer of scales on both 
sides of the wing; the under layer usually consisting of 
white ones. If you denude the wings of any butterfly, 
which you may easily do by scraping it lightly on both 
sides with a penknife, you will be amused to trace the 
lines in which the scales were planted, consisting of in- 
numerable minute dots: the lines of the under side, in 
some cases, so cut those of the upper side, as by their 
intersection to form lozenges. - With regard to the po- 
sition of the scales on the wing, they usually lie flat, but 
sometimes their extremity is incurved: in the beautiful 
Argynnis Vanille a very singular appearance of nume- 
rous transverse ridges is produced by the extremity of 
those scales that cover the longitudinal nervures of the 
primary wings, except at the base, being recurved. 
But though the general clothing of the wings of Le- 
pidoptera consists of these little scales, yet in some cases 
they are either replaced by hairs or mixed with them. 
Thus, in the clear parts of the wings of Heliconians, At- 
tacit, &c., short inconspicuous hairs are planted; in a 
large number of the Orders the wzpper side of the Anal 
Area of the secondary wings is hairy; in several Crepus- 
culars (Sphina Phenix, &c.), where there is a double 
