OF EPPING FOREST. 167
Imago.
Very variable, not distinguishable from A. quadrilineatus.
The A. albopunctata galls may become wrinkled when old, and
in some cases they adhere to the bud axis. They appear at the
end of April; mature very quickly, falling to the ground in May,
and occasionally not until June. The flies emerge in the
following spring, or sometimes not until April of the second
year. The eggs are laid in the buds about the middle of April.
OCCURRENCE IN EPPING FOREST.
Fairly common, but not so much so as in many places. They
have very much the appearance of buds, and on this account may
be easily passed over without notice. First appearance noted,
April 29th.
Genus BIORHIZA (Westwood).
The two generations of this genus are exceedingly alike, and,
in some cases, could scarcely be differentiated, except that in
the sexual forms, the male is never apterous or with the wings
rudimentary, and the female is usually furnished with wings,
though sometimes these may be absent, or only present in a
partially developed state.
The colour in both forms is yellowish brown.
There is, so far as we know, only one European species,
Biorhiza aptera-terminalis (Fab.)
The great resemblance which exists between Biorhiza
terminalis and B. aptera extends to the ovipositors also, although,
as a rule, among the Cynipidae the ovipositors differ even when
the other parts are almost, if not quite, identical. The difference
between ovipositors is due to the method of oviposition, which
varies according to the position in which the egg is to be laid;
in this case the position of the egg is very different in the two
generations, but as the method employed in depositing the egg
does not differ, the form of ovipositor remains the same in each
case. The great likeness which exists between so many different
species of this family is due to want of difference in their mode
of life, so that surroundings cannot act upon them to alter their
characters, the chief variations occurring in the gall instead.
This accounts for the similarity in outward appearance
between the sexual forms of the genus Dryophania and the
corresponding forms of the genus Neuroterus, which were at one