In the female the 7th sternum is very large, and its posterior extremity is cleft medianly in the adult (imago). The two halves are boat-shaped, and are connected by a distensible soft skin. They retain the egg-capsule, which the female carries about for a long time. The 8tn and 9th sterna are internal, and bent at an angle inter se. The 8th has the vaginal aperture. There are three pairs of processes in connection with these sterna, homologous with the parts of the oripositor in e.g. a Cricket, or of the sting of a Bee. The first pair, according to Huxley, are developed from the 8th, the second and third from the 9th sternum. The 10th sternum in the female appears to be obsolete. The anus opens terminally in both sexes, and lies between two triangularpodical plates, probably representing an 11tn somite, as in the Dragonfly. At the outer angles of these plates arise two many-jointed setose appendages, the cerci anales, or cercopoda, supposed by Packard to represent a pair of rudimentary abdominal legs.
The nervous system consists of a supra-oesophageal ganglion supplying the antennae, translucent white spots, eyes and labrum, and connected by very short commissures to an infra-oesophageal ganglion supplying the mandibles, maxillae, and labium. The ventral chain consists of three thoracic and six abdominal ganglia, united by double commissures. The oesophageal commissures have under the neurilemma a continuous layer of ganglion cells, and from them spring the two roots, one on each side, of the ganglion frontale. The ventral commissures also contain ganglion cells1. The stomatogastric system consists (1) of an azygos ganglion frontale, triangular in shape, lying in front of the supra-oesophageal ganglion, and giving off posteriorly a nervus recurrens, which courses along the dorsal wall of the oesophagus and crop; (2) of a couple of paired ganglia, lying on either side of the nervus recurrens anteriorly, and connected to the under side of the supra-oesophageal ganglion and to the nervus recurrens; (3) of a triangular ganglion terminating the nervus recurrens, from which two nerves, one on either side, run obliquely down the walls of the crop, and end in the muscular walls of the gizzard. Each nerve, near its termination, has a small ganglionic enlargement.
There is also a sympathetic system in connection with the ventral chain. A fine nerve springs from either the right or left commissure, connecting successive ventral ganglia, and about midway between the ganglia. It runs dorsally between the commissures, and just above the ganglion behind its place of origin it divides. Each branch swells into a long spindle-shaped ganglion, and then joins the lateral nerve of the same side coming from the ventral ganglion.
1 According to Nussbaum a ridge of cells is developed from the hypoblast in the embryo PeriWith the exception of the chylific stomach, the digestive tract is lined by a chitinous cuticula, which is for the most part beset with setae. The chitinous coat is continued into the salivary ducts and receptacles. In the ducts it is striated, as in the tracheae (infra). The finest branches of the ducts in the acini of the gland are smooth-walled, and their terminal dilatations are lined by a coat which is not chitinous. The walls of the digestive tract consist of an external membrane underlain by an outer layer of circular, and an inner layer of longitudinal1 striated muscle-fibres. Then follows a layer of connective tissue cells, and a layer of columnar cells, which secrete the internal cuticula where it is present. The chylific stomach is lined by columnar cells, with a striated border and rounded glandular cells lying in depressions. The gizzard has on its internal surface six longitudinal projections or teeth, and behind each tooth two cushions, the first with an uneven, the second with an even surface. In the interval between two teeth are three parallel folds, and between each of these and the teeth a smaller fold.
The posterior part, which projects into the chylific stomach, contains six principal folds in a line with the cushions, and between each of them a small accessory fold. The circular muscle layer is strongly developed, and according to Wilde, longitudinal fibres run from the teeth to the cushions, and on the outer surface of the posterior part, whilst radial fibres are found only in the anterior and posterior parts. The same authority states that in some Orthoptera the internal cuticula is cast off at each moult. According to Krukenberg (Untersuchungen Physiol. Inst. Heidelberg, ii. 1882, p. 26), the salivary glands secrete a purely diastatic ferment, the chylific stomach both diastatic, peptic and tryptic ferments. The ridges in the rectum consist of elongated hypodermis cells, underlain by a mass of connective tissue cells, richly supplied with tracheae. They are structures highly developed in the larvae cf Dragon-flies. These animals take in and expel water from the rectum, which thus becomes an important respiratory organ.
The Malpighian vessels consist of an outer homogeneous layer, a single layer of gland cells with large ramified nuclei, and internally a porous chitinoid (?) membrane. The secretion contains (1) yellow-brown globules, which if numerous make the vessels opaque; (2) clear white globules; (3) uric acid crystals. The tubes open in Periplaneta into the lower portion of the chyliflc stomach, but in most Insecta into the intestine. Rathke, however, states that in Blatta Germanica they arise as outgrowths from the intestine.
Planeta, immediately beneath the ventral nerve-chain. These cells eventually ensheath the nervous structures. Nussbaum suggests that the ridge represents the chorda supraspinalis in Lepidoptera; cf. infra, p. 160.
1 There is pparently a contradiction in Basch's paper (cited below) as to the position, etc. of these 1 yers. Cp. pp. 241, 249, 252 of his paper.
The corpus adiposum, or fat body, is a whitish glistening tissue, arranged more or less in masses, and consists of cells containing oily drops, albuminous bodies, and in some cases uric acid. This tissue originates by proliferation from a layer of cells within the hypodermis, if the observations of Wielowicjski on Corethra are to be trusted. Sub-hypodermic cells have been described also by Viallanes in the larval Eristalis and Musca.