No. 376.] THE WINGS OF INSECTS. 233 
The typical arrangement of the wing-veins is often modified, 
also, by an anastomosis of two veins; that is, two veins will 
come together at some point more or less remote from their 
extremities and merge into one for a greater or less distance, 
while their extremities remain separate. This is illustrated in 
Nemoura (Fig. 8), where veins Scz and Rı anastomose. 
In the preceding chapter we suggested a nomenclature of 
the principal wing-veins and of their chief branches, which is 
applicable to all of the orders of winged insects. At that time 
nothing was said regarding the cross-veins; for it seems hardly 
Fic. 6. — Wing of a Leptid, showing veins a 
practicable to propose a nomenclature of these based on homolo- 
gies which shall have an equally general application. This arises 
from the fact that in those orders where the number of wing- 
veins is greatly increased, the primitive cross-veins, if such 
exist, are in most cases indistinguishable from those that have 
been developed secondarily. 
But when we examine the wings of those orders in which the 
tendency is towards a reduction in the number of wing-veins, 
we find that there are a few cross-veins which are so constant 
in their position and which occur in so many widely separated 
groups that they are evidently homologous. As the number 
of these is small, we propose to designate them by names, as 
follows: 
The humeral cross-vein. This is a single cross-vein extending 
from the subcosta to the costa near the humeral angle of the 
wing (Fig. 6,4). This is the most constant of all of the cross- 
veins, | 
