OF EPPING FOREST.
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It is narrowed toward the apex at which is situated the
papilla (g).
The posterior plate (e) is also narrowed towards the apex and
broad at the base.
The sheath (h) is made up of two pieces which together
form a groove in which the two spiculae, or boring apparatus
proper, can move.
These spiculae (f) are attached to the triangular plate and
are usually toothed at the apex.
The five muscles-which are attached to the plates act on
the posterior plate by contraction and expansion, giving the
spiculae a backward and forward movement.
The egg itself consists of a round egg body (Fig. 4, m)
which eventually contains the embryo, and a long stalk-like
process (k) which is useful in two ways. During the process of
oviposition the egg body is not sent down inside the ovipositor,
but the egg-stalk is clasped and carried down by the two
spiculae, the main portion of the egg remaining outside, as the
groove inside the sheath is not large enough to admit it.
In the case of such galls as Biorhiza terminalis, when the egg
is laid in the bud, a passage is first formed by the insect down to
the cambium layer. The egg, when it reaches the extremity of
the ovipositor, is not detached from the spiculae, but the egg
body is placed at the mouth of the groove formed in the bud
from which the ovipositor is partially withdrawn and pushed
down until it reaches the cambium layer. The ovipositor is
furnished with a number of tactile hairs whereby the insect is
kept informed, as it were, of the progress of the egg to its proper
destination.
Besides acting as a means of attachment to the spiculae
by which the latter can seize the egg, the egg tube is also
used as a respiratory organ whereby oxygen can be admitted to
the embryo developing in the interior of the embedded egg body,
For this purpose it is left lying in the canal formed by the
insect previously to the deposition of the egg. One insect may
lay from six hundred to seven hundred eggs, and oviposition
may extend over a period of three or four days. As before
mentioned the egg must be laid in the cambium layer, which
envelopes the whole of the plant and represents the growing
zone. Eggs laid in winter buds are particularly liable to failure,