THE FUNCTIONS OF A LOCAL NATURAL HISTORY SOCIETY. 25 
nail galls of the lime and those of the American vine, the former 
the work of mites, and the other of a dipterous insect or Cecidomya, 
both being formed on the upper surface of the leaves. On 
cutting them open, it will be found that while the cavity of the 
insect-gall contains only one larva, the mites always form a 
large colony. Some of these mite-galls resemble externally those 
of insects, while others look like dust or powder, and at one time, 
as no grub could be found in any of them, the mites being 
so minute and transparent that it is necessary to break them up, 
tease them out in water, and examine the washings under the 
microscope to find them, it was supposed that these formations 
were due to the fungi, and the different kinds were described by 
fungologists as the genus Erineum. A common example of the 
mite-galls is the so-called clusters of the ash, in which the mites 
have attacked the pistils of the flower bud, and the irritation 
has produced such a growth of woody tissue that when dry they 
require a saw to divide them. 
Among insects, gall-makers are found in the following orders, 
viz. :--Hymenoptera, Diptera, Coleoptera, Hemiptera, and Lepidop- 
tera ; but before giving examples of these, there are a few general 
facts to which I should like to direct your attention. Of course, 
the ravages of the gall insects affect the health of the plant itself, 
and frequently destroy the branch or bud which is attacked ; but, 
as in every other animal and plant, Nature provides means of 
checking their excessive development and consequent destruction 
of the food-plant, they being all subject to the attacks of parasites, 
and thus the balance of nature is preserved. 
I have already spoken of the Inquilines or insects which take 
advantage of the gall already produced to lay their eggs in, and 
so procure suitable food for their larvz, as is done in this country 
in the common oak apple by the Tortrix, Coccyx obscurana. But 
in addition to this, all these larve are subject to the attacks of 
small parasitic Hymenoptera, the females of which are provided 
with long ovipositors ; these are inserted into the galls, and the 
skin of the larve pierced sufficiently to allow one or more eggs to 
be introduced ; these hatch, and while the host larva is feeding 
