THE WINGS OF INSECTS. 
J. H. COMSTOCK AnD J. G. NEEDHAM. 
CHAPTER IV. 
The Specialization of Wings by Addition. 
I. THE DEVELOPMENT OF ACCESSORY VEINS. 
THE more important of the generalizations reached in the 
course of the present investigation are two in number ; first, 
the recognition of certain features of the venation of the wings 
of insects, which occur in the more generalized forms of a large 
proportion of the orders of this class, has enabled us to present 
a hypothetical type to which the wings of all orders may be 
referred ;! second, if we leave out of consideration the anal 
area, that portion of the wing traversed by the anal veins, we 
will find that in nearly every case each order of insects is char- 
acterized by either a reduction or a multiplication of the wing- 
veins ; in certain orders the tendency is in one direction, 
while in others it is in the opposite ; but either of these tend- 
encies may be correlated with a similar tendency in the anal 
area or with the opposite one. 
In the preceding chapter we pointed out the various ways in 
which the number of the wing-veins in the preanal area is 
reduced. In nearly every case we found the reduction of the 
preanal area accompanied by a similar tendency in the anal 
area, or, if a reduction had not taken place, there was no 
increase in the number of veins of this area, the tendency 
being towards the production of a few-veined wing. The Tri- 
choptera, however, form an exception to this rule. 
We have now to consider several types of wings, in each of 
which there is taking place an increase in the number of veins 
of the preanal area, the tendency being towards the formation 
of a many-veined wing. In speaking of an increase in the 
number of veins, reference is made only to a multiplication 
1 American Naturalist, vol. xxxii (February, 1898), pp. 81-89. 
