Fig. 271.—Under side of Agrionid nymph, with short mask, living in water in lilies. Hawaiian Islands. × 3.
The Odonata have no close relations with any other group of Insects. They were associated by Latreille with the Ephemeridae, in a family called Subulicornia. The members of the two groups have, in fact, a certain resemblance in some of the features of their lives, especially in the sudden change, without intermediate condition, from aquatic to aerial life; but in all important points of structure, and in their dispositions, dragon-flies and may-flies are totally dissimilar, and there is no intermediate group to connect them. We have already, said that the Odonata consist of two very distinct divisions—Anisopterides and Zygopterides. The former group comprises the subfamilies Gomphinae, Cordulegasterinae, Aeschninae, Corduliinae, and Libellulinae,—Insects having the hinder wings slightly larger than the anterior pair; while the Zygopterides consist of only two subfamilies—Calepteryginae and Agrioninae; they have the wings of the two pairs equal in size, or the hinder a little the smaller. The two groups Gomphinae and Calepteryginae are each, in several respects, of lower development than the others, and authorities are divided in opinion as to which of the two should be considered the more primitive. It is therefore of much interest to find that there exists an Insect that shares the characters of the two primitive subfamilies in a striking manner. This Insect, Palaeophlebia superstes (Fig. 272), has recently been discovered in Japan, and is perhaps the most interesting dragon-fly yet obtained. De Selys Longchamps refers it to the subfamily Calepteryginae, on account of the nature of its wings; were the Insect, however, deprived of these organs, no one would think of referring Palaeophlebia to the group in question, for it has the form, colour, and appearance of a Gomphine Odonate. Moreover, the two sexes differ in an important character,—the form of the head and eyes. In this respect the female resembles a Gomphine of inferior development; while the male, by the shape and large size of the ocular organs, may be considered to combine the characters of Gomphinae and Calepteryginae. The Insect is very remarkable in colour, the large eyes being red in the dead examples. We do not, however, know what may be their colour during life, as only one pair of the species is known, and there is no record as to the life-history and habits. De Selys considers the nearest ally of this Insect to be Heterophlebia dislocata, a fossil dragon-fly found in the Lower Lias of England.
Fig. 272.—Palaeophlebia superstes. A, The Insect with wings of one side and with two legs removed; B, front view of head of female; C, of male. (After De Selys.)
Numerous fossil dragon-flies are known; the group is well represented in the Tertiary strata, and specimens have been found in amber. In strata of the Secondary age these Insects have been found as far back as the Lower Lias; their remains are said to exist in considerable variety in the strata of that epoch, and some of them to testify to the existence at that period of dragon-flies as highly specialised as those now living. According to Hagen[[347]] Platephemera antiqua and Gerephemera simplex, two Devonian fossils, may be considered as dragon-flies; the evidence as to this appears inadequate, and Brongniart refers the latter Insect to the family Platypterides, and considers Platephemera to be more allied to the may-flies.
One of the most remarkable of the numerous discoveries lately made in fossil entomology is the finding of remains of huge Insects, evidently allied to dragon-flies, in the Carboniferous strata at Commentry. Brongniart calls these Insects Protodonates,[[348]] and looks on them as the precursors of our Odonata. Meganeura monyi was the largest of these Insects, and measured over two feet across the expanded wings. If M. Brongniart be correct in his restoration of this giant of the Insect world, it much resembled our existing dragon-flies, but had a simple structure of the thoracic segments, and a simpler system of wing-nervures. On p. [276] we figured Titanophasma fayoli, considered by Scudder and Brongniart as allied to the family Phasmidae, and we pointed out that this supposed alliance must at best have been very remote. This view is now taken by M. Brongniart himself,[[349]] he having removed the Insect from the Protophasmides to locate it in the Protodonates near Meganeura. There appears to be some doubt whether the wings supposed to belong to this specimen were really such, or belonged rather to some other species.
CHAPTER XIX
AMPHIBIOUS NEUROPTERA CONTINUED—EPHEMERIDAE, MAY-FLIES
Fam. VII. Ephemeridae—May-flies.