Kinsey: Gall Wasp Genus Cynips 
53 
the Atlantic seaboard, retaining its long wings everywhere 
except in the most remote corner of its range, in the very 
southeastern corner of the United States, where it is now de- 
veloping short-winged species. 
There are a few further aspects of the distribution of 
Cynips which have some bearing on the problem of species. 
1. The maps of the several species show that ranges vary 
from relatively small (e.g. the San Bernardino area of Cali- 
fornia and the Apache Trail area of Arizona) to very large 
(e.g. the whole of Central Europe or the northeastern quar- 
ter of the United States), but they more often involve areas 
of considerable size. This means that species are relatively 
stable entities which are not easily disturbed by mutations 
or immigrations of new stocks. If such new stocks are not 
submerged, interbreeding must proceed fast enough over these 
areas to maintain the uniformity of the species. It is diffi- 
cult to conceive how this can occur in the largest of the areas. 
2. The ranges of these species are more often large in the 
regions which are topographically most uniform. The rela- 
tively rugged Central European area is an exception to this 
rule. Nevertheless, the general condition indicates that the 
isolation afforded by topographically diverse areas may be a 
considerable factor in favoring the multiplication of species. 
3. There are, on the other hand, areas of relatively uni- 
form topography within which distinct species have been iso- 
lated. This is true of the Canadian, Coastal Plain, northern 
Middle West, southern Middle West, Ozark, east Texas, and 
Central Texas areas in the United States. None of these 
areas appears to be bounded in such a way as to furnish 
enough geographic factors to isolate species. Distance must 
be an isolating factor in the origin and propagation of species. 
This item is never listed among factors of distribution, but I 
am inclined to believe that in an area like the eastern United 
States it is one of the most important factors. Distance 
would act as a barrier by preventing an interchange of genes 
thruout a large population, thus favoring the development of 
local races. 
4. Another fact showing the importance of isolation is the 
common occurrence of hybrid individuals in transition areas 
between species. These hybrid populations are so extensive 
in the more uniform, eastern two-thirds of the United 
