340 THE AMERICAN NATURALIST. 
in Rhamphomyia (Fig. 37) it has proceeded so far that vein 
Cu2 extends towards the base of the wing, and presents the 
appearance of a cross-vein. 
It is not strange that the homology of the branches of the 
cubitus in forms like Rhamphomyia was not understood until 
the method of study used here was employed, but now there is 
no doubt regarding it. 
The independent specialization of different parts of the 
wing can be seen by comparing members of the two series 
given above. Compare, for example, Thereva (Fig. 32) with 
Pantarbes (Fig. 34). If one were to consider only the degree 
of coalescence of veins Cuzz and Zsż A, Thereva would be con- 
sidered the more highly specialized of the two genera, for in 
this genus these two veins coalesce for a considerable distance, 
while they are still distinct in Pantarbes. But if the degree of 
coalescence of veins M} and Cz; be considered the opposite 
conclusion would be reached, for in Pantarbes these veins 
coalesce for the greater part of their length so that cell 47, is 
completely obliterated, while in, Thereva these veins are still 
distinct. No better evidence could be desired for showing the 
impossibility of arranging animals in a natural linear series. 
And it is not too much to hope that an exhaustive study along 
these lines will serve to determine the phylogeny of the fami- 
lies of this order. 
pa LABORATO 
CORNELL rE. a 1898. 
