232 THE AMERICAN NATURALIST. [VOL. XXXII. 
insects of the Linnean order Neuroptera in having a much 
smaller number of wing-veins than is possessed by them. 
These differences indicate two different methods of speciali- 
zation by which this primitive type has been modified: the one, 
specialization by reduction; the other, specialization by addi- 
tion. 
We postpone any farther reference to the latter method of 
specialization and confine our attention in this place to a study 
of some of those forms in which a tendency to modify the 
primitive type by a reduction in the number of wing-veins is 
evident. 
A reduction in the number of wing-veins takes place in two 
ways: first, by atrophy of veins; second, by the coalescence of 
two or more adjacent veins. 
The first method is illustrated in most of the orders where a 
reduction in the number of wing-veins has taken place by the 
atrophy, more or less complete, of one or more of the anal veins; 
this is correlated with a reduction in the extent of the anal 
area. This method is also illustrated in certain cases where 
there is no apparent reduction of the area of the wing from 
which the vein has disappeared. The most familiar illustrations 
of this occur in the Lepidoptera. In this order, as is well 
known, the main stem of the media disappears in many families; 
and in the geometrid moths of the family Eunomidz, the second 
branch of this vein is also lost. 
The second method of reduction — that is, by coalescence — 
takes place in all of the orders in which the number of wing- 
veins is less than in the typical wing. This also takes place 
in two ways: first, the point at which two veins separate occurs 
nearer and nearer the margin of the wing, until finally, when 
the margin is reached, a single vein remains where there were 
two before; second, the tips of two veins may approach each 
other on the margin of the wing until they unite, and then the 
coalescence proceeds towards the base of the wing. The former 
is a coalescence extending outward; the latter, a coalescence 
extending inward. Examples of the former are common in all 
of the orders discussed in this chapter; illustrations of the latter 
are most easily observed in the Diptera, 
