FIG. 3.--Median section through mid-body of female Red Ant (_Myrmica rubra_). H, Head; 1, 2, 3, the thoracic segments; i., ii., the first and second abdominal segments; i., being the propodeum.] _Characters._--In all Hymenoptera the mandibles (fig. 1, C, D) are well developed, being adapted, as in the more lowly winged insects, such as the Orthoptera, for biting. The more generalized Hymenoptera have the second maxillae but slightly modified, their inner lobes being fused to form a _ligula_ (fig. 1, B, b). In the higher families this structure becomes elongated (fig. 2, g) so as to form an elaborate sucking-organ or "tongue." These insects are able, therefore, to bite as well as to suck, whereas most insects which have acquired the power of suction have lost that of biting. Both fore- and hind-wings are usually present, both pairs being membranous, the hind-wings small and not folded when at rest, each provided along the costa with a row of curved hooks which catch on to a fold along the dorsum of the adjacent fore-wing during flight. A large number of Hymenoptera are, however, entirely wingless--at least as regards one sex or form of the species. One of the most remarkable features is the close union of the foremost abdominal segment (fig. 3, i.) with the metathorax, of which it often seems to form a part, the apparent first abdominal segment being, in such case, really the second (fig. 3, ii.). The true first segment, which undergoes a more or less complete fusion with the thorax is known as the "median segment" or _propodeum_. In female Hymenoptera the typical insectan ovipositor with its three pairs of processes is well developed, and in the higher families this organ becomes functional as a sting (fig. 5),--used for offence and defence. As regards their life history, all Hymenoptera undergo a "complete" metamorphosis. The larva is soft-skinned (eruciform), being either a caterpillar (fig. 6, b) or a legless grub (fig. 7, a), and the pupa is free (fig. 7, c), i.e. with the appendages not fixed to the body, as is the case in the pupa of most moths. [Illustration: FIG. 4.--Fore-Wings of Hymenoptera. 1. Tenthredinidae (_Hylotoma_)-- 1, marginal; 2, appendicular; 3, 4, 5, 6, radial or submarginal; 7, 8, 9, median or discoidal; 10, sub-costal; 11, 12, cubital or branchial; and 13, anal or lanceolate cellules; a, b, c, submarginal nervures; d, basal nervures; e, f, recurrent nervures; st, stigma; co, costa. 2. Cynipidae (_Cynips_). 3. Chalcididae (_Perilampus_). 4. Proctotrypidae (_Codrus_). 5. Mymaridae (_Mymar_). 6. Braconidae (_Bracon_). 7. Ichneumonidae (_Trogus_). 8. Chrysididae (_Cleptes_). 9. Formicidae (_Formica_). 10. Vespidae (_Vespa_). 11. Apidae (_Apathus_).]