INSECT GALLS 
is originated by the act of ovipositing. In the case 
of the Cynipid galls, however, it has been clearly 
demonstrated that gall production does not commence 
until the larvae begin to feed. 
The following is a list of some of the commoner 
species of Zoocecidia found in this locality: 
Order ACARINA. 
A large number of the galls in this group are still 
unclassified, but the type characters are well marked. 
The different species constitute a clear phylogenetic 
series from the simple erineum to the well-developed 
pouch gall. The distinction between the different 
members of this series is largely a difference in degree 
rather than in kind, and seems to be explainable on 
the assumption of a gradually increasing intensity 
of stimulus from the lowest to the highest member 
of the series. A simple erineum type is that found 
on the underside of the leaves of Fagus grandifolia, 
Ehrh., while Hriophyes abnormis, a pouch gall on 
the leaves of Tilia americana, L., stands at the other 
end of the series. As an average between these 
extremes may be placed such a form as the “ dimple ” 
gall on the leaves of Quercus macrocarpa, Michx. 
Order Hemiptera. 
These galls are characterized by a folding and 
wrinkling of the leaf when they occur on that organ, 
and in this particular resemble the types of the pre- 
ceding section. 
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