i8o 
TRANSFORMATIONS OF INSECTS. 
growth, it makes a very woody cocoon, and sticks it to the twigs 
of the tree upon the leaves of which the insect lives. The cocoon is 
brown and very hard, and the larva hybernates in it, and is trans- 
formed in the spring. The fly gnaws off the top of the cocoon 
from within, and escapes ; its jaws, like those of most others, 
being made solely for this purpose. The Tom-tits get a great 
many of the larvae by nibbling the cocoons during hard winters. 
THE HYMENOPTERA WHICH PRODUCE GALLS. 
GALL FLIES ( Cynipsidce ). 
The Hymenoptera that produce galls, or excrescences upon 
plants, form a group by themselves. They are small insects, 
very distinguishable, and they stimulate a great number of dif- 
ferent kinds of plants to develop those unusual growths of their 
tissues which are called gall-nuts, galls, oak-apples, &c. Every- 
body has seen these curious and odd-looking excrescences ; but 
very few have noticed the beings that have grown within them — 
and which, when they have attained their perfect form, escape 
and fly. A winged insect not much more than a tenth or a 
twelfth of an inch long is not readily observed, especially when 
amongst the host of little flies that continually move around us. 
These small Hymenoptera belong to one family — that of the 
Cynipsidce — which contains the genus Cynips , and others very 
much like it. The Cynipsidce have an oblong and very convex 
body, the abdomen of which is attached to the thorax by a very 
thin pedicle. The saw ovipositor is very curiously made ; it is 
very long and slender, and is twisted up in a spiral form within 
the abdomen of the female when it is not required. But when 
the insect has made up its mind to lay an egg, having chosen 
the proper spot, the muscles of the abdomen suddenly unfold 
this spiral, and the ovipositor is straightened, and thrust instan- 
taneously into the plant. 
The Cynipsidce are found everywhere in spring and summer. 
When about to lay, the females take great trouble to seek a 
good place on a proper plant : they make a puncture with their 
long ovipositors in a twig or leaf, and deposit either one or a 
