Page:Phylogeny of cynipid genera and biological characteristics.pdf/5

 But in Diastrophus and Rhodites we find both an arcuate and an angulate condition occurring in the same genus, though the differences between two species at the extremes of variation within the genus are not to be compared with the extreme differences which occur between the genera. Apparently the form of the first abscissa of the radius gives evidence not only of group descent but also of the evolution of the species within a genus. Such a complete set of data, interpreted in the light of other evidence, should prove of great value for discovering an arrangement of the species of the family which will indicate the natural order of relationships.

The problem with which we are now confronted is to discover where in the series was the starting point, the primitive condition of deciding in which direction development has proceeded. If, in trying to solve this question, we seek evidence in the related families of Hymenoptera, we find that apparently very little help is to be obtained there. In the Figitidæ, which are mainly parasitic species, every species of the hundreds I have examined shows an arcuate vein, which is one of the extremes to be found in the Cynipidæ. Shall we assume that the gall-wasps have originated from the more primitive figitids or that the figitids have originated from the most highly specialized of the cynipids? I think that the story might be read with equal justice in either direction if the whole of our information came from the wing-venation. In the arcuate vein we might picture the remnants of two veins of an ancestral, a more primitive, a more abundant vein condition, the two veins still evident and not entirely fused in those species showing an angulate vein. On the contrary, it is reasonable to believe that the angulate vein is the more developed condition: if this is truly the radial vein, it is a longitudinal vein and the projection at the apex of the angle is a cross-vein even though it extends lengthwise of the wing. The addition of such crossveins to a primitive venation is not an unknown thing, though we have not realized that such additions occur very often among the Hymenoptera. Moreover, we have no great warrant in believing that this projection on the radial vein is really a vein; it is not to be distinguished from chitinizations which occur in the wings of many other Hymenoptera, and I cannot see good reasons for believing that the projection in this case is to be considered a vein rather than some other sort of formation.

It is to be expected that, where such limited considerations are drawn upon, the interpretations may be made in diametrically opposite fashions and we need not be impressed with either set of interpretations