BUTTERFLIES OF MAINE. 9 
are extended, is called the costa or anterior margin; the 
angle at the outer end of the costa is called the apex, and 
the side which follows, being the most remote from the body 
when the wings are extended, is called the outer margin 
(hinder margin of some authors); the angle which follows 
is called the anal angle, and the side of the wing extending 
from the anal angle to the body, is called the hinder margin 
(inner margin of some authors). 
Those veins of the wings, usually four in number, which 
go out from the base may be called nervures. The one near- 
est the costa is called the costal nervure ; the next behind this, 
the subcostal nervure; the next in order extending approxi- 
mately through the middle of the wing, and dividing it into 
two more or less equal parts, is called the median nervure ; 
the one behind this last is called the submedian nervure ; and 
a short one, occurring in some species behind the submedian 
is the internal nervure. 
The first and last two of these extend to the margin of the 
wing, but the subcostal and medium nervures extend out to 
near the middle of the wing where they are joined by a vein 
which is called the transverse nervure. The remaining veins 
are branches of the subcostal and median nervures, or extend 
out from the transverse nervure, and are ealled nervules. 
We make use of the term veins when we wish to use a word 
to include either or both nervures and nervules, and we call 
the whole veiny structure of the wing the venation. 
The system of numbering the veins adopted very generally 
by European entomologists, and to some extent in this country, 
is to number them in order at their terminations along the 
margins of the wing, whether nervures or nervules and with- 
out regard to their length. The vein going out from the 
base of the wing below the median, is called number 1. If, 
however, there are two, as the internal nervure and the sub- 
median, then the first is called 1 a, and the second 1 b. The 
first branch of the median is number 2, the second, number 
3, and so on around the outer margin and costa to the costal 
