_Ichneumonoidea._--The ten thousand known species included in this group agree with the Cynipoidea and Chalcidoidea in the position of the ovipositor and in the jointed trochanters, but are distinguished by the fore-wing possessing a distinct stigma and usually a typical series of nervures and areolets (figs. 4, 8). Many of the species are of fair size. They lay their eggs (fig. 8) in the bodies of insects and their larvae belonging to various orders. A few small families such as the _Evaniidae_ and the _Stephanidae_ are included here, but the vast majority of the group fall into two large families, the _Ichneumonidae_ and the _Braconidae_, the former distinguished by the presence of two median (or discoidal) cells in the fore-wing (figs. 4, 7), while the latter has only one (figs. 4, 6). Not a few of these insects, however, are entirely wingless. On account of their work in destroying plant-eating insects, the ichneumon-flies are of great economic importance. _Proctotrypoidea._--This group may be distinguished from the preceding by the position of the ovipositor at the extreme apex of the abdomen, and from the groups that follow (with very few exceptions) by the jointed trochanters of the legs. The pronotum reaches back to the tegulae. The _Pelecinidae_--included here by Ashmead--are large insects with remarkably elongate abdomens and undivided trochanters. All the other members of the group may be regarded as forming a single family--the _Proctotrypidae_, including an immense number of small parasitic Hymenoptera, not a few of which are wingless. Of special interest are the transformations of _Platygaster_, belonging to this family, discovered by M. Ganin, and familiarized to English readers through the writings of Sir J. Lubbock (Lord Avebury). The first larva is broad in front and tapers behind to a "tail" provided with two divergent processes, so that it resembles a small crustacean. It lives in the grub of a gall-midge and it ultimately becomes changed into the usual white and fleshy hymenopterous larva. The four succeeding sections, in which the ovipositor is modified into a sting (always exserted from the tip of the abdomen) and the trochanters are with few exceptions simple, form the _Aculeata_ of Linnaeus. _Formicoidea._--The ants which form this group are readily distinguished by the differentiation of the females into winged "queens" and wingless "workers." The pronotum extends back to the wing-bases, and the "waist" is greatly constricted and marked by one or two "nodes." The differentiation of the females leads to a complex social life, the nesting habits of ants and the various industries that they pursue being of surpassing interest (see ANT).