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Indiana University Studies 
with the 1905 publication shows a typical Q. alba leaf. The 
occurrence of a true Cynips gall on any tree of the black oak 
group is inconceivable to one who has critically observed the 
host distribution of cynipid genera ill general. 
The type material of erinacei, from north-central Ohio, rep- 
resents an insect with a dark rufous head which is prominently 
marked with black on the mid-line, with antennae which are 
rufous only on the first two segments, a dark rufous mesono- 
tum, and a piceous black abdomen which is dark rufous ba- 
sally. This combination of characters is represented by insects 
in our collections from nearly one hundred localities scattered 
all the way from southern Maine and Minnesota to south- 
western Virginia and Missouri, but in practically all of these 
localities such insects have been obtained from both naked 
and spiny forms of the gall, and from every conceivable inter- 
mediate type of gall. The extreme variation of the gall is 
matched, moreover, by the variation of the insects in every 
large series which we have from localities representing the 
wide range of erinacei . The significance of this variation is 
elucidated by the occurrence of true wheeleri as one extreme 
of these variable series and (in most places) of derivatus as 
the other extreme of each series. Usually the wheeleri and de- 
rivatus individuals are few in comparison to the intermediates, 
but from Meadville, in the northwestern corner of Pennsyl- 
vania, we have 107 insects of which 41 per cent show distinct 
wheeleri influence, 37 per cent derivatus practically identical 
with the Alabama and Georgia material of that variety, and 
21 per cent good erinacei. This series, like all the others, 
shows every gradation from wheeleri to derivatus, and the 
types called erinacei are matched by individuals near the mean 
of the series. There is little room to question that erinacei 
has come from the hybridization of wheeleri and derivatus , 
probably effected when the Pleistocene glaciation forced the 
sub-Canadian variety southward into the range of derivatus. 
Upon the retreat of the glaciers, the hybrid found a great ter- 
ritory in the northern Middle West where it was sufficiently 
isolated from the rest of the species to gradually assume, thru 
the endless inbreeding of the hybrid individuals, a certain 
homogeneity which warrants its taxonomic recognition. Eri- 
nacei is much like a West Indian or Northern African mulatto 
people (to illustrate from two very different types) which, 
originating from white and black crosses, and so isolated as to 
