256 THE AMERICAN NATURALIST. [VoL. XXXII. 
migrated away from the spur indicating its more primitive 
position, and that the medio-cubital cross-vein (m-cu) is no 
longer transverse, but appears to be a continuation of the main 
stem of the cubitus. 
VII. THE VENATION OF THE WINGS OF TRICHOPTERA. 
In the preceding pages much evidence has been given to 
show the importance of studying the trachez that precede the 
wing-veins, in order to determine with certainty the homologies 
of the latter. But in some of the orders of insects a remark- 
Fic. 27. — Wing of a pupa of a caddice fly. 
able reduction of the wing tracheze has taken place, which 
renders them useless for this purpose. This is true of the 
Trichoptera and Diptera, and also to a considerable extent of 
the Hymenoptera. 
If the wing of a pupa of a caddice fly be examined at that 
stage when the forming wing-veins appear as pale bands, it will 
be seen that the tracheation of the wing bears but little relation 
to the wing-veins. Usually only two or three main trachez are 
present; and although these may coincide with forming veins, 
their branches bear no relation whatever to veins (Fig. 27). 
Fortunately, in the case of the Trichoptera we do not need 
to study trachez in order to determine the homologies of the 
wing-veins; for here, in the more generalized members of the 
order, we find the primitive type of wing venation well preserved. 
