rm to which Ganin compares it. It may
be described as bearing a general resemblance to the third and fully
developed larval form (Fig. 196, _tg_, three pairs of abdominal
tubercles destined to form the sting; _l_, rudiments of the legs; _fk_,
portion of the fatty body; _at_, rudiments of the antennae; _fl_,
imaginal disks, or rudiments of the wings). No tracheae are developed in
the larva, nor do any exist in the imago. (Ganin thinks, that as these
insects are somewhat aquatic, the adult insects flying over the surface
of the water, the wings may act as respiratory organs, like gills.) It
lives six to seven days before pupating, and remains from ten to twelve
days in the pupa state.

The origin of the sting is clearly ascertained. Ganin shows that it
consists of three pairs of tubercles, situated respectively on the
seventh, eighth, and ninth segments of the abdomen (Fig. 196, _tg_). The
labium is not developed from a pair of tubercles, as is usual, but at
once appears as an unpaired, or single organ. The pupa state lasts for
five or six days, and when the imago appears it eats its way through a
small round opening in the end of the skin of its host, the Agrion
larva.

[Illustration: 197. Development of Egg-parasites.]

The development of Ophloneurus, another egg-parasite, agrees with that
of Platygaster and Polynema. This egg-parasite passes its early life in
the eggs of Pieris brassicae, and two or three live to reach the imago
state, though about six eggs are deposited by the female. The eggs are
oval, and not stalked. The larva is at first of the form indicated by
figure 197 _E_, and when fully grown becomes of a broad oval form, the
body not being divided into segments. It differs from the genera already
mentioned, in remaining within its egg membrane, and not assuming their
strange forms. From the non-segmented, sac-like larva, it passes
directly into the pupa state.

The last egg-parasite noticed by Ganin, is Teleas, whose development
resembles that of Platygaster. It is a parasite in the eggs of Gerris,
the Water Boatman. Figure 197 _A_ represents the egg; _B_, _C_, and _D_,
the first stage of the larva, the abdomen (or posterior division of the
body) being furnished with a series of bristles on each side. (_B_
represents the ventral, _C_ the dorsal, and _D_ the profile view; _at_,
antennae; _md_, hook-like mandibles; _mo_, mouth; _b_, bristles; _m_,
intestine; _sw_, the tail; _ul_, under lip or labium.) In