572 HYMENOPTERA didoe and Oxyura, which are normally winged, occasionally appear in an apterous or semi-apterous condition. On the anterior margin of the hind wings are placed a number of very minute hooks, which fit into a thickened rim on the posterior margin of the front wings, so that the two become united, and strike the air as one whole. The wings are usually transparent, and, in certain arrangements of the light, are seen to be highly iridescent. Occasionally they are coloured in patches, or are entirely black or blue ; in the latter case, they are not unfrequently of a thickish texture and have a metallic lustre, as, e.g., in Hylotoma. The smaller forms (ChalddldcK and Oxyura] have few or no nervures. Some of these have the wings deeply fringed ; ) 1, marginal ; 2, appenclicular; 3, 4, 5, 6, sub- . . . 10. Diploptera ( Vespa). 11. Anthophilia (Apathus). and Mymar audFlalrinus have the wings as it were cleft and stalked ; that is to say, there is a long, thin stalk projecting from the thorax for a certain distance ; then it dilates into a number of deeply fringed branches (see fig. 5). The head is seldom broader than the thorax. It is usually of a more or less globular shape, but may be much flattened and long. The compound eyes are placed along the sides, while the simple eyes, or ocelli, are arranged in a triangle on the vertex. Certain ants and Chalcididce are blind. Others have eyes, but want the ocelli. The mouth organs are, except with bees, adapted solely for mastication or for prehension ; while, in addition to performing these functions, wasps use them for building up or digging out their nests in the ground or wood. Some worker ants and other aculeates (especially males) have the mandibles enor mously developed. Mastophaga, an insect found in figs, has a curious mandible, remarkable, not in itself, but by having attached to it an appendage whose use is supposed to be to clean away the juice of the fig from the mouth. The maxilla and labiuni are provided with jointed palpi. The number of joints in the maxillary palpi is usually five, but may be more or less than that ; the labial palpi are two- to four-jointed. It is with bees that the mouth parts (and especially the ligula) have their greatest development and specialization. With them the various parts (except the mandibles) are elongated to form a sucking tube, by means of which they lap up the nectar of flowers. The form of the antennae is very variable. They may Antem have three (Hylotoma) to sixty joints (ichneumons); may be very long and thin as in ichneumons, or scarcely projecting beyond the head as in Perga ; of uniform thickness, or dis tinctly clavate as in Cimbex; bare, or very hairy. Then they often differ very much in the males. Lophyrus (Tenthre- dinidce) and many Chalcididw have them pectinated in various degrees ; they are deeply forked in Schizocera ; and many others have them covered with long hair, although they are quite bare in the other sex. In some families the number of joints varies very much, but most Aculeata have the same number, namely, 13 in the male and 12 in the female. These appendages serve as sense organs, especi ally for the discovery of food, and, in the male, for finding the female. At any rate an ichneumon (for instance) when searching for a larva in which to lay its eggs (and this has especially been noticed with those which oviposit in concealed larvae) keeps them in a state of continuous trembling motion, arid males have also been observed to do the same when searching for the females. The three divisions of the thorax pro-, meso-, and meta- Thora: thorax have pretty much the same relative proportions in all the families. The prothorax is small. The upper part is strongly articulated to the mesothorax, while the lower is freer ; and it is by means of this lower part that the head is united to the thorax. The metathorax is very large, as might be expected, from its having to take such an import ant part in flight. As for the scutellum it varies more than any other portion of the thorax. Mostly it is flat, or at least only slightly raised above the mesonotum ; but in the smaller groups (Oxyiira, Chalcididce, Cynipidai) its form is sometimes very curious. In jEgilips (Cynipidce) and Agriotypes (Ichneumonidce) it is produced into a sharp more or less curved spine ; in Eucoela it is cup-shaped, that is to say, it is raised up, and has the centre hollow. It undergoes, however, its greatest development with some ChalcididcK. In Chirocerus, for example, it is lengthened so much that it reaches the middle of the abdomen. The metathorax is never very large, nor does it exhibit any marked peculiarities. The legs show the same manifold diversity in form that Legs. we found to exist with the other appendages. The basal parts thecoxse and trochanters are not usually of any size, except in the lower tribes, e.g., Chalcididce. In classifica tion the trochanters are of value, for we find with tha Aculeata they are joined to the femora by a single joint, whereas in all the other Hymenoptera there are two joints. Hence the bees, wasps, &c., form the division Monotrocha ; and the ichneumons, saw-flies, <fcc., are denominated Ditrocha. Some Chalcididce have the femora greatly thickened, and toothed on the under side ; x but as a rule it does not show any striking peculiarity unless it be with some male insects. As might be expected from their more intimate connexion with the habits of the insects, the tibia) and tarsi vary according to the uses they are put to, apart from locomotion. With bees (at least with the non-parasitie species) they are employed to carry the pollen necessary for the nourishment of the young ; for this purpose they are 1 The enormous development of the hind femora in Chalcis and Leucaspis does not appear to give these insects extra leaping power. Other Chalcididce which have not thickened femora can leap consider
able distances.
