On account of the great extension of the metathorax and the haunches of the large hindlegs, the first abdominal sternite is wanting, and the second is - the stylets.
The larvae have the three pairs of legs well developed, and the hinder abdominal segments swollen.
The fourth abdominal segment is often very large, and forms the greater part of the hind-body; this segment is markedly constricted at its basal (forward) end, where it is embraced by the small third segment.
Abg, Abdominal ganglion.
N, First Abdominal Segment.
- This is an important tribe of beetles, including families with four malpighian tubes and only five or six abdominal sterna, while in the thorax there is a backwardly directed process of the prosternum that fits into a mesosternal cavity.
Ab, Abdominal ganglion or site pe, The right pedal nerve.
In Hemiptera only eleven and in Collembola only yolk, and that the mesenteric epithelium becomes reinforced by six abdominal segments have been detected.
The nervous system is remarkably concentrated in some beetles, the abdominal ganglia showing a tendency to become shifted forward and crowded together, and in certain chafers all the thoracic and abdominal ganglia are fused into a single nervecentre situated in the thorax, - a degree of specialization only matched in the insectan class among the Hemiptera and some muscid flies.
The number of spiracles is greatly reduced; in the adult a pair is present on the mesothorax, sometimes also a pair on the metathorax, and there is always a pair on the first and another pair on the eighth abdominal segment.
The young insect resembles its parent in most points, but the head is disproportionately large; the anterior abdominal spiracles are on the second segment instead of on the first, and the foot has only a single segment.
Their abdominal bones are like those of the marsupials; and they are furnished with pouches for their young, but have no teats, the milk being distilled into their pouches from the mammary glands.
The left hepatica magna receives also the umbilical vein, which persists on the visceral surface of the abdominal wall, often anastomosing with the epigastric veins.
In male beetles, however, the two pairs of genital processes (paramera) belonging to the ninth abdominal segment are always present, though sometimes reduced.
The well-known "fire-flies" of the tropics are large click-beetles (Elateridae), that emit light from paired spots on the prothorax and from the base of the ventral abdominal region.
Lameere's classification is founded on the number of abdominal sterna, the nervuration of the wings, the number of malpighian tubules (whether four or six) and other structural characters.
They may be distinguished from the Malacodermata by the presence of only five or six abdominal sterna, while six malpighian tubes are present in some of the families.
The female is a segmented, wormlike creature, spending her whole life within the body of the bee, wasp or bug on which she is parasitic. One end of her body protrudes from between two of the abdominal segments of the host; it has been a subject of dispute whether this protruded end is the head or the tail, but there can be little doubt that it is the latter.
The insects of this order have mandibles adapted for biting, and two pairs of membranous wings are usually present; the first abdominal segment (propodeum) becomes closely associated with the fore-body (thorax), of which it appears to form a part.
The peculiar form and arrangement of the anterior abdominal segments have already been described.
In many of those ants whose third abdominal segment forms a second " node," the basal dorsal region of the fourth segment is traversed by a large number of very fine transverse striations; over these the sharp hinder edge of the third segment can be scraped to and fro, and the result is a stridulating organ which gives rise to a note of very high pitch.
The hinder abdominal segments and the stings of the queens and workers resemble those of other stinging Hymenoptera.
In these ants the difference between the large, heavy, winged males and females, and the small, long-legged, active workers, is so great, that various forms of the same species have been often referred to distinct genera; in Eciton, for example, the female has a single petiolate abdominal segment, the worker two.
The euthyneurous visceral loop is long, and presents only one ganglion (in Aplysia camelus, but two distinct ganglia joined to one another in Aplysia hybrida of the English coast), placed at its extreme limit, representing both the right and left visceral ganglia and the third or abdominal ganglion, which are so often separately present.
In some cases, however, it can be shown that the cerci really belong to an eleventh abdominal segment which usually becomes fused with the tenth.
The first and second abdominal sterna are often suppressed or reduced, on account of the strong development of the hind-legs.
In many insects ten, and in a few eleven, abdominal segments can be clearly distinguished in addition to a small terminal anal segment.
A marked modification of the hinder abdominal segments may be noticed in most insects, achynematus).
- Outline of Male (a') and Female (?) Cockroaches (Blatta) from the side, showing Abdominal Segments (numbered I-b).
8), and as many as eight distinct pairs of abdominal ganglia may often be distinguished, the hindmost of which represents the fused ganglia of the last four segments.
Paired processes on the eighth and ninth abdominal segments may be specialized as external organs of reproduction, but these are probably not appendages.
The female genital opening usually lies in front of the eighth abdominal segment, the male duct opens on the ninth.
The legs, wings and other organs of the trunk receive their nerves from the thoracic and abdominal ganglia, and the fusion of several pairs of these ganglia may be regarded as corresponding to a centralization of individuality.
The ganglia become greatly changed in position during the later life, and it is usually said that there are only ten pairs of abdominal ganglia even in the embryo.
A, Abdominal ganglia in the streptoneurousvisceral commissure, with supraand sub-intestine ganglion on each side.
26, b, c) can be brought close together so as to form a club-like termination; usually the hinder abdominal segments are not covered by the elytra.
Coprolites have been found at Lyme Regis, enclosed by the ribs of ichthyosauri, and in the remains of several species of fish; also in the abdominal cavities of a species of fossil fish, Macropoma Mantelli, from the chalk of Lewes.
From two to four moults occur, after which the " pronymph " stage is reached, which in the insect is moderately active and possesses wing-rudiments reaching to the second abdominal Segment.