Kinsey: Gall Wasp Genus Cynips 59 
three types of insects at Meadville is, however, the picture of 
segregation from a hybrid population which continues to pro- 
claim its parentage. Similar series of erinacei are in our 
collections from many other localities. 
There is, of course, a ready explanation of a past contact 
of wheeleri and derivatus . If wheeleri was in existence dur- 
ing the Pleistocene glaciation, its range must have been 
pushed southward at least as far as southern Indiana and the 
Ohio River, and still further south in the eastern mountains. 
If the range of derivatus at that time was comparable to the 
range of the present-day species, wheeleri first hybridized with 
derivatus in the Ohio Valley and in the valleys adjacent to 
the southern Appalachians. But as the glaciers retreated to 
the north, wheeleri retreated with them, leaving derivatus far 
to the south, and a tremendous area between where the hybrid 
wheeleri x derivatus found its opportunity to breed and inter- 
breed until it had acquired the uniformity which warrants 
its present recognition as a species. 
The Pleistocene origin of erinacei finds confirmation in 
three other hybrid species of Cynips in the same Northeastern 
area of the United States. These species are Cynips fulvicollis, 
C. gemmula, and C. macrescens. The detailed data are pre- 
sented in the systematic portion of this study. They parallel 
the case of erinacei. These four cases account for all of the 
stocks of Cynips which are known to have penetrated far 
enough into the Northeast to have developed sub-Canadian 
varieties which would have been alfected by the Pleistocene 
glaciation. These four cases are the only ones among the 93 
species of Cynips which we now have reason for believing of 
hybrid origin, except for C. advena, of the Cumberland High- 
lands, which we shall show in a moment to date also from the 
Pleistocene. Of all the areas occupied by Cynipidae in the 
United States, this Northeastern area, the Eastern mountain 
country, and areas immediately adjacent to these are the 
only ones which had a Pleistocene history that would have 
provided the opportunity for the multiplication of hybrid 
individuals and which would have offered a subsequent isola- 
tion sufficient for the origin of new species. The apparent 
restriction of the hybrid Cynips to those areas seems con- 
firmation of our explanation. 
The fifth case C. advena, which we have mentioned, in- 
