Fossils.—Abundant remains of Phryganeidae belonging to the Tertiary epoch have been discovered. They are common in amber, and it is a remarkable fact that a larval case has been found in amber. This seems almost inexplicable, except on the assumption that such larvae were of arboreal habits, a condition that, at the present time, must be excessively rare, though the terrestrial habits of Enoicyla warrant us in believing it may occur. In the Tertiary Lake Basin at Colorado the remains of Phryganeidae in the imago state are extremely abundant, so that it is curious that but few such remains have been found in Europe. In Auvergne the so-called indusial limestone, which is two or three yards thick over a wide area, is considered to be composed chiefly of the cases of larvae of this family.
In the Mesozoic epoch some wings found in the lower Purbeck strata are considered to be those of Phryganeidae; similar wings have been found in the Lias, but this is the only evidence of the existence of the family at that period except a tube, supposed to be a larval case, detected in the Cretaceous of Bohemia. Earlier than this nothing has been discovered that can be connected with the family, so that at present the palaeontological evidence appears unfavourable to the view held by some that the Phryganeidae may be considered forms allied to the early conditions of the Lepidoptera. It should be noted that the head in Phryganeidae is the most important part from a systematic point of view, and that fossils have been chiefly identified from the wings; this is a much more doubtful character, as the wings of the Phryganeidae have a simple system of neuration, and in shape have nothing very characteristic.
Extinct Order Palaeodictyoptera.
This seems to be the fittest place to notice the existence of some fossil remains from the Palaeozoic rocks that cannot be fitly, or certainly, assigned to any of our existing Orders, and to which the above name has consequently been given. These remains consist chiefly of wings in a more or less imperfect state of preservation, and it is therefore quite doubtful whether the course of assigning them to a separate Order supposed to be extinct be correct. This is all the more doubtful when we recollect that an Insect fossil, Eugereon bockingi, having the head with mouth-parts of a Hemipterous or Dipterous nature, has been found, the wings attached to it being such as, had they been found separate, would have been considered to be Neuropterous, or at any rate allied thereto. About forty-two forms of Palaeodictyoptera are assigned by Scudder to a section called Neuropteroidea, and may therefore be considered to have a special resemblance to our Neuroptera. These Neuropteroidea comprise numerous genera and no less than six families. Scudder's view is at the best tentative, and is not very favourably received by some entomologists. Brauer has, indeed, objected altogether to the formation of this Order Palaeodictyoptera, and Brongniart has published a list of the Palaeozoic Insects in which a system of arrangement different to that of Scudder is adopted. In his most recent work[[408]] Brongniart assigns some of these Neuropteroidea to the families Platypterides and Protodonates, which we have previously discussed. The whole subject of these Palaeozoic Insect remains is still in its infancy, and it would not be proper to accept any view as final that has yet been stated, nor would it be fair to dismiss the subject as unimportant because of the great divergence of opinion amongst the authorities who have investigated it.
CHAPTER XXII
HYMENOPTERA—HYMENOPTERA SESSILIVENTRES—CEPHIDAE—ORYSSIDAE—SIRICIDAE—TENTHREDINIDAE OR SAWFLIES
Order IV. Hymenoptera.
Wings four, membranous, without scales, usually transparent, never very large, the posterior pair smaller than the anterior; the cells formed by the nervures irregular in size and form, never very numerous (less than twenty on the front, than fifteen on the hind, wing). Mandibles conspicuous even when the other parts of the mouth form a proboscis. The side-pieces of the prothorax are disconnected from the pronotum and overlap the prosternum, usually entirely concealing it. The females are furnished at the extremity of the body with either saw, sting, or ovipositor; these parts may either be withdrawn into the body or be permanently protruded. The metamorphosis is great and abrupt, the chief changes being revealed in the pupa disclosed at the last moult of the larva; this moult is frequently delayed till long after growth has been completed. In the pupa the parts of the perfect Insect are seen nearly free, each covered in a very delicate skin.
The term Hymenoptera includes ants, bees, wasps, sawflies, and the tribes of innumerable Ichneumon-flies. The Order is of enormous extent, consisting even at present of tens of thousands of described and named species, and yet these are but few in comparison with those that remain unknown. It has good claims to be considered the "highest" Order of Insects. Sir John Lubbock says: "If we judge animals by their intelligence as evinced in their actions, it is not the gorilla and the chimpanzee, but the bee, and above all the ant, which approach nearest to man."[[409]] The mechanical perfection of the structures of the individuals, and the rapid and efficient manner in which their functions are discharged, are very remarkable. In many species of Hymenoptera the individuals have the habit of living together in great societies, in which the efforts of the members are combined for the support of the whole society and for the benefit of a younger generation. To fit them for this social life the bodies of the larger number of the individuals are more or less changed in structure, so that they become workers. These workers are in all cases imperfect females; besides carrying on the ordinary work of the society, they tend and feed the young. The duty of reproduction is restricted to a single female, called a queen, or to a small number of such individuals in each society. The males occupy an unimportant position in the society, and are usually much shorter-lived than the workers and queens. The social Hymenoptera do not form a single zoological group, but are of three different kinds—wasps, bees, and ants. There are numerous non-social, or solitary, wasps and bees.
