280 OAK GALLS AND GALL INSECTS
The meta-thorax is very small, though the pleural and sternal regions and
the meta-notal stigma are quite distinct.
(5.) The median segment, though in reality the first abdominal segment,
forms in the Cynipina and other Hymenoptera, a fourth thoracic segment.
It is, as it were, separated from the abdomen by the petiole, and is often con-
founded with the meta-thorax. In reality the petiole is the second abdominal
segment. The stigma of the median segment may be larger, foveate or
reticulate.
(6.) Legs. Of moderate size. Trochanters bi-articulate. There are
either one or two spurs on the fore tibiae, and on the hind tibiae there are
two unequal spurs. The Metu-tarsus is long and the tarsi are four-jointed.
Claws may be simple or cleft
Patella seldom conspicuous.
Fig. 5. Andricus collaris (Htg.) Perfect insect, magnified. An example
of the Sub-Family Cynipina.
(7.) The Abdomen varies much in form. It maybe slender or thick, long
or ovate. Sometimes it appears to be nearly sessile, which is due to the shape
of the patiole.
According to Cameron there are seven abdominal segments, which
differ in length, especially the second and third, a point much used in
classification. The apical ventral segment may be ploughshare shaped. The
number of segments in the abdomen differs with different authors according
to whether they consider the medium segments or the petiole to be the first
abdominal segment. In reality the median segment is. If this latter view is
taken the abdomen consists of eight instead of seven segments, the varying
segments being the third and fourth. There are only six visible segments on
the ventral region of the female, and five in the male.
The Ovipositor, which has been previously described, has its origin close to
the base of the abdomen.