More striking, however, are the species in this genus which are hardly distinguishable except by gall characters. It seems valid to recognize taxonomic groups based on such hereditary, physiologic characters if they involve large populations with distinct host relations and distinct geographic ranges. Nevertheless, current taxonomic studies are so often established upon morphologic bases that they would not recognize such species as the 24 physiologic Cynips listed above. In consequence we have seen much confusion of biologic data and serious invalidation of important conclusions.
Some of these physiologic species of Cynips deserve especial mention.
1. Cynips maculosa and C. mirabilis are hardly distinct insects, altho their galls (figs. 207-210) are very distinct. These two stocks have been separated since early in the history of the subgenus, but it is certain that most of their evolution has involved physiologic capacities of the insects.
2. Insects of Cynips echinus echinus and C. echinus douglasii seem absolutely indistinguishable. That the galls are very distinct is evident from figures 154-158.
3. Insects of Cynips echinus schulthessae and C. echinus vicina are very similar. A comparison of figures 151-153 and 156-158 will show how characteristic the galls of such species may be.
4. All of the European Cynips would certainly be considered three species on the basis of either the bisexual insects, the bisexual galls, or the agamic insects. The three would be Cynips folii-longiventris, C. divisa-disticha-cornifex, and C. agama, with the last not entirely distinct. I am convinced that without the distinctive galls (figs. 125-137) of the agamic forms of these insects they would never have been recognized as the six specific stocks which they really represent.
5. The insects of Cynips nubila appear identical with those of C. russa. The two galls (figs. 299-300) are alike in all respects except color. Nubila galls are wine-purple; those of russa are yellowish-russet. The first occurs in Arizona south of Tucson, the other north of Tucson (fig. 58). They occur on the same hosts (Q. arizonica and Q. oblongifolia), and occur within a few miles of each other at places in their ranges. The data do not warrant the admission of seasonal, climatic, or host factors as explanation of the differences in gall color. The two represent extensive populations existing in adjacent but distinct geographic areas, and must be considered as species. One of these species must have originated from the other by mutation as abrupt as that which gave rise to the short-winged species treated in the preceding section of this paper.
6. Cynips multipunctata conspicua and C. multipunctata heldae are hardly distinct insects, altho their galls are strikingly unlike in external form (see figs. 203 and 205-206). The close relations of the two are