THE LEPIDOPTERA. 69 
At first sight the scales look like dust, and they come off on 
to the finger and thumb when the wings are touched; but under 
the microscope they present most elegant shapes and singularly 
elaborate details of structure. Variable according to the genera 
and species of the Lepzdoptera, and equally so in different parts of 
the same wing; the scales may be more or less elongated or even 
fan-tailed in shape, and rounded at the free edge, or incised, so 
as to resemble dentations or pointed festoons. There is a short 
stalk at the base of each scale, which resembles a handle under 
the magnifying power of the microscope, and it is the portion 
A PORTION OF THE WING OF Adtacus pavonia major. 
Showing the method of implantation of the wing scales. (Magnified. ) 
which is implanted into the alar membrane. The surface of 
the scales ordinarily presents several longitudinal keel-like promi- 
nences, which are parallel and equidistant. Some cross markings, 
which are very close together, form a very delicate network 
between the keel-shaped lines, and they appear to have some- 
thing to do with the connection between the neighbouring scales. 
The scales are formed by two layers of excessively delicate tissue, 
and the colours are produced by extremely small dots, beads, or 
corrugations, which act upon the rays of light, and produce the 
phenomena of “interference.” There is no special colouring matter 
in the scales, and all the effect is brought about by the “ 
ference” and decomposition of light. Dr. Pigott and others have 
lately shown that the so-called ribs of the scales are corrugations 
of one or both of the layers of tissue, and that the beads—which 
inter- 
