58 
Indiana University Studies 
tions in every large series which we have from nearly a hun- 
dred localities well spread over the range. 
The interpretation of this population has become possible 
thru the discovery of its closest relatives, Cynips wheeleri to 
the north and Cynips derivatus to the south of the area 
occupied by erinacei (see map, fig. 63). Erinacei occurs 
exactly where we might expect a hybrid of wheeleri x deriv- 
atus origin. 
Wheeleri is a uniformly small insect; derivatus is large; 
ermacei shows every gradation between the extremes. 
Wheeleri is largely black; derivatus is prominently rufous 
over most of the body; erinacei shows every sort of combina- 
tion and recombination of these characters. The mesonotum 
of wheeleri is largely smooth and naked; the mesonotum of 
derivatus is rough and more hairy than in any of the related 
species; the mesonotum of erinacei varies from smooth and 
more naked to rough and hairy, again showing every grada- 
tion and combination between the supposed parents. The 
galls of wheeleri are ellipsoidal, polythalamous, and uniformly 
spiny; those of derivatus are spherical, one- or two-celled, 
and uniformly naked; the galls of erinacei (figs. 312-315) 
show these extremes and a remarkable series of every con- 
ceivable intermediate between and combination of these ex- 
tremes. Detailed descriptions of the insects are given in the 
systematic portion of this study. Remembering that many 
of these characters are probably controlled by multiple factors 
in heredity, erinacei appears as just that variable combina- 
tion of characters which we might expect from a wheeleri x 
derivatus cross. 
This interpretation finds confirmation in such series as the 
107 insects which we have from Meadville, in the north- 
western corner of Pennsylvania. In this series 41 per cent 
of the individuals show clear evidence of wheeleri affinities, 
37 per cent are practically identical with our Alabama and 
Georgia material of derivatus, and 21 per cent show grada- 
ations between wheeleri and derivatus that would pass as 
good erinacei. It is certain that erinacei is not of present- 
day origin, for wheeleri and derivatus are separated thruout 
most of their ranges by several hundreds of miles. This dis- 
tance is too great to allow any present-day hybridization of 
pure stocks of wheeleri and derivatus. The occurrence of the 
