Page:The Gall Wasp Genus Cynips.pdf/98

 we might recognize a third species, because the bisexual insects of divisa in Central Europe are easily enough distinguished; but the situation remains as shown in the following diagram where similarities are indicated by arrows, the agamic insects by, and the bisexual insects by ♀ ♂.

On the other hand, from galls alone, European Cynips would be granted six or seven species, which would recognize no distinctions (on galls alone!) between northern and more southern material. Graphically, this may be shown (where ⊕ is the gall) as follows:

If we take into account both insects and galls, which should we use for establishing specific lines, and which for varietal lines? Our procedure may be determined by the fact that between the galls of the six types there are no intergrades, while between the northern and Central European insects there are numerous intergrades. This suggests that each northern insect has been derived by variation and geographic isolation from a Central European insect, and that the galls remain as indicators of the ancestry of these variants, i.e. that the galls in the subgenus Cynips should be taken to indicate the specific, and the insects the varietal lines of a natural classification. The conclusion finds abundant corroboration in our American experience with geographic variation; and European students are not likely to dissent with a solution that does no more damage than this to the previous classifications. The