576 HYMENOPTERA larva is succeeded by a third, which differs from it in being longer and thinner, while the various organs have reached a further stage of advancement in complexity of structure. The after course of its development does not differ from that of other Hymenoptera. Polynema and Mymar (egg- parasites) go through somewhat similar changes in their early embryonic life. Classification. As regards the classification of the Hymenoptera, the order divides itself naturally into two great divisions, as has been already indicated. The Aculeata form a division distinguished alike by the form of the sting, with its connected poison-bag, and by the trochanter being joined to the femur by a single joint. The other division (that usually called Terebrantia or Ditrocha) has a double joint to the trochanter, and the ovipositor is never used as a weapon of offence. The Ditroi ha are again divided into two sections, well distin guished by the form of the abdomen, by the larva, and by habits : the one (the Securifcra) has the abdomen sessile, the larvae have legs, and they are phytophagous ; while the other (the Spiculifera) has the abdomen petiolated, the larvae are apodal, and they are (except part of the Cynipidcc) animal feeders. The Securifcra are further distinguished from all others by the form of the ovipositor, which forms either a short "saw," as in the Tenthredinidce, or a stout exserted "borer," as in the Siricidce ; and they have another peculiarity in having at the bottom of the anterior wing a cellule, termed the " lanceolate cellule " (see fig. 1, above), which is found in no other family, and is of great use in classification. The Securifcra embraces the families Tenthredinidce and Siricidce (by some Cephus is made into a third family, while by others it is placed among the Tenthredinidce, owing to its agreeing with the saw-flies in the form of the thorax and ovipositor, and by others with the Siricidce, because it has only one spine in the anterior leg, while the saw-flies have two). The species of Siricidce are few in number, and have a very wide distribution. They are larger than any Tenthredinidce, and are indeed among the giants of the order. All live in wood, especially in Conifcrce, and have occasion ally done great damage to the forests in Germany. As they are easily imported along with timber, they very often make their appearance in out-of-the-way places and frighten ignorant people, although, of course, they are perfectly harmless. The Spiculifera contain the families Cynipidce, Chalcididce, Proc- totrypidce, Evanidcc, Braconidce, and Ichneumonidce. The Cynipidce, or gall-flies, are small insects, rarely exceeding two lines in length. The antennoa are straight, inserted in the middle of the face ; the joints are variously shaped, and do not exceed 16 in number. The thorax is large ; the scutellum always forms a con spicuous object, and its form is very varied. The abdomen is much compressed, especially with the males ; curled up over the apical segments is the long thin bristle-like ovipositor. A few species are apterous. There is always a radial cellule in the anterior wing, but few nervures and there is never a stigma. What distinguishes the Cynipidce more especially is their habit of raising galls on plants to serve as food and lodgings for their young. 1 These galls have the most diversified shapes, and are raised on all parts of a plant the buds, leaves, roots, flowers, and fruit all being used by the gall insects. A gall may serve to shelter a solitary larva, or it may be so large as to contain many hundreds. The oak is the principal tree used by the Cynipidcc ; next is the rose, upon which is found the well-known " bedeguar gall " of llhodites rosce, once used medi cinally ; the maple, poppy, bramble, hawkweed, and some other plants have likewise their galls. All Cynipidce, however, are not gall-makers. One group deposit their eggs in the galls raised by the true gall-makers, when they are soft and young, and the larva of the cuckoo-fly lives on the gall at the expense of the legitimate owner, which is killed by the more energetic intruder. Another group contains pure animal feeders, parasites which live at the expense of other insects (especially plant lice). Closely allied to the Cynipidce is the family Chalcididce, an immense tribe of very minute insects with brilliant metallic green bodies. Their wings have few nervures, and they never form closed cellules, but a stigma is always present. The antennae are always elbowed ; they have never more than 13 joints, and may have as few as 6. With the males they are sometimes flabellate, or covered with tufts of hair. Generally the ovipositor is short and concealed, but it may be exserted and much longer than the entire body. In cither case it issues from the lower side of the belly. Apterous arid semi-apterous species are not uncommon. In habits the Chalcididce 1 There is a radical distinction between the gall-making Cynipidce and the gall- making saw-flies. The latter feed on the gall itself, so that in course of time it becomes reduced to a mere bladder; and the gall is tully formed before the larva leaves the egg. On the other hand, the development of Ci/nips and the growth of the gall go on at the same time, the reason of this being that it feeds only on the juice of the gall, which hardens and dries very soon after it makes its appearance, so that necessarily the larva has to feed up rapidly. After the gall has dried the larva occupies a cell of harder matter than the rest of the gall, not much larger than its own bulk. are very diversified. They are parasites on insects of all orders and in all stages. While no definite line can be drawn, yet particular groups in the mass confine their attacks to certain families of insects. Thus Leucaspis and Ckalcis are attached to bees and other nest- building aculeates, the long-tailed Torymides to oak and other galls, the Encry tides to Ilomoptera (Coccus especially). Species of Isosoma appear to be herbivorous, and one in America is destructive to corn, by raising gall-like structures at the joints and thus causing the plant to wither. Giraud has likewise described Isosoma to be a vegetable feeder, at any rate during a considerable portion of its life, as well as another species (Aulogymnus aceris) which lives in galls on the maple. Those curious forms, Sycophaga and Blastophaga, which live in figs, appear undoubtedly to feed on their seeds. The species of Proctotrypidce (called also Oxyura), unlike those of the Chalcididce, are dull-coloured insects, usually entirely black, or at best relieved by brown or red. They are distinguished from the last family by the non-elbowed antennae, which are 8- to 13- jointed. The wings in the smaller forms may be without nervures, while in the higher they are much more developed than in the Chalcididce. The edges of the wings are deeply fringed with some species ; and other species have dense patches of hair on the thorax and abdomen. One group bears raptorial claws on the front tarsi; and, in connexion with this structure, it is worthy of notice that the late A. H. Haliday observed one species to kill and deposit in an empty straw a caterpillar, apparently for the purpose of laying its eggs in it ; so that in habits it approximates to the fossorial Hymenoptera, which some of them undoubtedly do in structure. The Oxyura are parasites. Some are attached to gall insects, others to aphides, while Diptera and eggs of insects of all orders afford nourishment to many. The insects usually called " ichneumons " belong to two families the Ichneumonidce and Braconidce. Both are readily distinguished from the families already mentioned by the wings being well pro vided with nervures, which form regular cellules, by the greater number of joints in the antennae, and generally by their much greater size. The only radical distinctions between the groups are that the Ichneumonidce have two recurrent nervures, and a little joint in front of the second antennal joint, whereas this is absent in the Braconidce, which have besides only one recurrent nervure. In habits there is no broad distinction between them. They are para sites on insects of all orders. The Evanidce are a small and some what heterogeneous assemblage of insects, which do not agree very well in their structure ; but the typical species may be known by the abdomen being inserted in the middle or above the middle of the metathorax. As far as is known the family are parasitic on cock roaches, and appear to be not very numerous in species. In some respects the Chrysididce are intermediate between the Aculeata and the Terebrantia, for they have the single-jointed tro chanter of the former, while in the structure of the ovipositor, in having the antennae 13-jointed in both sexes, as well as in habit, they agree with the latter. They are exceedingly brilliant insects ; their bodies are metallic, with shining green, purple, or golden hues. The abdomen hangs as it were from the thorax, and is somewhat concave on the under side. It can be bent under the thorax, so that the insect can roll itself up into a ball, which is its way of protect ing itself when attacked its hard metallic coat of mail being im pregnable against the mandibles of other insects. These insects differ from other terebrant Hymenoptera in the structure of the abdomen, for it has never more than four segments visible in the female and five in the male, while the ichneumons have always more. The terminal segments form a tube, which is used in oviposition. In habits the Chrysididce, do not differ from the ichneumons, being parasites. They prey principally on bees and wasps, whose nests they enter when the owners are absent, and should they be dis covered their hard skin saves them from serious injury. Indeed the only portions of their bodies which can be mutilated are the wings. St Fargeau observed a bee do this to a chrysis ; she bit off the four wings, but did not thereby save her young, for as soon as the bee left, the now wingless parasite crawled into the nest and laid her eggs therein. As has been stated, the Aculeata are distinguished from all other Hymenoptera by having a sting, a single-jointed trochanter, and the antennae with 12 joints in the female and 13 in the male. They differ, too, in habits from the Terebrantia, for, although many of them are parasites, their parasitism is unlike that of the ichneumons. Parasitic Aculeata earn their bread differently : they enter the nests of other aculeate species and lay their eggs in the food stored up there for the benefit of the young of the builder, which are starved or destroyed by the more vigorous larva of the parasite. In order to carry out their ends with greater ease, some parasites mimic the forms of the species upon which they prey. Thus Apatlius rupcstris is coloured exactly like Bombus lapidarius, its host. On the other hand the species of Nomada, an extensive genus of parasitic bees, do not resemble in the least the bees on which they prey ; they have instead gaudily coloured, hairless bodies. One of the most interest ing chapters in the history of the Aculeata is their nest building.
The nests are built in all sorts of places and of all kinds of materials.
