Fig. 278—Zaitha anura, carrying eggs on its back. West Indies.
Fig. 279—Antenna of Belostoma sp. A, One side of the under surface of the head, with antenna, b, extended; B, with the antenna retracted, a, Side of head; c, pocket for antenna; d, position of the eyes. The corresponding joints of the antenna are numbered 1, 2, 3, 4 in each figure.
They appear to be unable to resist the attraction of artificial light, and are consequently sometimes destroyed in large numbers. It has long been known that species of the genera Diplonychus and Zaitha carry their eggs on their backs. There is no special receptacle for the purpose, but the eggs are kept in their peculiar position by means of a cement insoluble in water. It has been stated by Dimmock that they are placed in position by means of a long, flexible ovipositor. Schmidt, however, found that a specimen of Diplonychus, bearing eggs and examined by him, was a male, and he subsequently found that this was the case with other egg-bearing individuals of other species, so that the mode in which the eggs are placed in this position and the object of so curious a habit, remain uncertain. The species of Belostoma are highly remarkable on account of the curious and complex structure of their antennae, in respect of which the nearest analogy is to be found in the large Coleoptera of the genus Hydrophilus. A very deep, ear-like pocket, exactly suited to the form of the antennae, exists on the under side of the head; hence in repose no sign of the peculiar shape of the antennae exists. When the antennae are placed in this ear-like pocket only the one side of the basal joints is exposed, the long processes being received into the deep pocket. In Hydrophilus the antenna is used as an accessory organ of respiration, and it will be interesting to learn whether this is also the case in Belostoma. Belostomidae have patches of air-carrying pubescence, analogous with those of Hydrophilus, on the under sides of the body, elytra and wings, but we do not know how they are charged. Another extremely interesting analogy is found in the manner in which the elytra are locked to the body; a projection from the thoracic side-pieces, forming a long pouch, into which a fold on the inner side of the elytra fits, the two being subsequently locked by the action of some special projections. This arrangement is similar to that which exists in the anomalous family of water-beetles Pelobiidae. In order to make this mechanism more perfect the side-pieces in Belostoma form free processes. Martin has informed us that the young have the metasternal episternum prolonged to form a lamella that he thinks may be for respiratory purposes.[[499]] About twelve genera and upwards of fifty species of Belostomidae are known. None exist in our isles, but several species extend their range to Southern Europe. In the waters of the warm regions of the continents of both the Old and New Worlds they are common Insects, but as yet they have not been found in Australia.
Fam. 24. Notonectidae.—Prosternum short, so that the legs are placed near the back part of it as well as near the front; back of the head overlapped by the front of the pronotum.—The water-boatmen are extremely common in our ponds, where they may be seen rising to the surface and raising the posterior extremity of the body for breathing. They swim on their backs instead of in the usual position, and have an elaborate arrangement of long hairs on the body to assist them to carry about an air-supply. They are said to be lighter than the water, and to have some difficulty in keeping away from the surface. Notonecta glauca is the only British species, but we have a second minute Insect, Plea minutissima, belonging to the family. It lies in the mud at the bottom of shallow waters, and may sometimes be fished up in great numbers. It is considered by some authors to form a distinct family. The oviposition of Notonecta has been observed by Regimbart; the eggs are inserted into the stems of aquatic plants.
Fam. 25. Corixidae.—Prosternum short, as in Notonectidae; summit of the head free from the thorax.—We have numerous species of the genus Corixa in Britain; and others extremely similar in appearance occur in various parts of the world. The head is remarkably free, and capable of great rotation. On dissection it is found to be attached to the thorax only by a narrow area; in this respect it differs widely from Notonecta, which possesses an extremely large occipital foramen, and the head of which possesses but little freedom of movement. The extremely short proboscis is more or less retractile, and therefore frequently appears absent. A second British genus consists of a single species, Sigara minutissima. These Insects, unlike Notonecta, are quite at home beneath the water, where they scurry about with extreme rapidity, and occur sometimes in enormous numbers. In Mexico the eggs of Corixa americana and of C. femorata are used as food, and are said to be very nice. The Insects themselves are used as food in both Mexico and Egypt. The species of this family can make a noise beneath the water by rubbing the front feet against the proboscis.[[500]] The males have a very complex asymmetry of the terminal segments, and in some species possess on one side of the dorsal surface a curious asymmetrical organ consisting of rows of very closely-packed, intensely black, comb-like plates, called by Buchanan White a strigil. This organ seems to be similar to the peculiar structures found on the terminal segments of certain species of Scutellerides.
Sub-Order II. Homoptera.[[501]]
Fam. 1. Cicadidae.—Head with three ocelli, placed triangularly on the summit between the compound eyes; antennae consisting of a short basal joint, surmounted by a hair-like process divided into about five segments. Front femora more or less thick, armed with teeth. Peduncle (or basal joints) of antennae without sensitive organs.—This important family consists chiefly of large Insects, few being as small as one inch across the expanded wings, while in some the expanse is as much as seven inches. As a rule the four wings are transparent and shining, with the nervures remarkably distinct and dark coloured; but there are numerous forms where the whole creature, including the wings, is highly pigmented in a showy manner; frequently in black and yellow. Cicadas are said to be without any special protection, and to be destroyed in considerable numbers by birds and other animals. The body is broad and robust, and is never shaped into the extravagant forms we meet with in some of the other families of Homoptera.
Fig. 280—Cicada septendecim. North America. (After Riley.) A, Larva; B, nymph; C, nymph skin after emergence of the imago, D; E, section of twig with series of eggs; F, two eggs magnified.