The Life-History and Anatomy of Butterflies 
rmles of many species have peculiarly shaped scales arranged in 
tufts and folds, which are called androconia, and are useful in 
microscopically determining species (Fig. 37). The portion of the 
wings which is nearest to the thorax at the point where they are 
attached to the body is called the base; the middle third of the wing 
is known as the median or discal area , the outer third as the limbal 
area. The anterior margin of the wings is called the costal margin; 
the outer edge is known as the external margin , the inner edge 
as the inner margin. The shape of the wings varies very much. 
The tip of the front wing is called the apex, and this may be 
rounded, acute, falcate (somewhat sickle-shaped), or square. The 
angle formed by the outer margin of the front wing with the inner 
margin is commonly known as the outer angle. The correspond¬ 
ing angle on the hind wing is known as the anal angle , and the 
point which corresponds to the tip or apex of the front wing is 
known as the external angle (Fig. 38). A knowledge of these 
terms is necessary in order to understand the technical descrip¬ 
tions which are given by authors. 
If a wing is examined with the naked eye, or even with a lens, 
a clear conception of the structure of the veins can rarely be 
formed. Therefore it is generally necessary to remove from the 
wings the scales which cover them, or else bleach them. The 
scales may be removed mechanically by rubbing them off. They 
may be made transparent by the use of chemical agents. In the 
case of specimens which are so valuable as to forbid a resort to 
these methods, a clear knowledge of the structure of the veins 
may be formed by simply moistening them with pure benzine or 
chloroform, which enables the structure of the veins to be seen 
for a few moments. The evaporation of these fluids is rapid, and 
they produce no ill effect upon the color and texture of the wings. 
In the case of common species, or in the case of such as are abun¬ 
dantly represented in the possession of the collector, and the 
practical destruction of one or two of which is a matter of no 
moment, it is easy to use the first method. The wing should be 
placed between two sheets of fine writing-paper which have been 
moistened by the breath at the points where the wing is laid, and 
then by lightly rubbing the finger-nail or a piece of ivory, bone, 
or other hard substance over the upper piece of paper, a good 
many of the scales may be removed. This process may be repeated 
until almost all of them have been taken off. This method 
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