Two lines are next supposed to extend vertically, one on each side, from between the seventh rib to the prominence formed by the large bone of the pelvis (Fig.1II., 6, 6). By these vertical lines the three first regions are still further subdivided in the follow ing manner :—The right and left parts of the Epigastric Region form two distinct regions (7,7) ; these arc termed the right and left Hypochondriac Regions (7, 7) ; while the central part retains the name of the Epigastric Region (3). In like man ner the right and left parts of the Umbilical Region form two distinct regions (8, 8), which are termed the Lumbar Re gions (8, 8), while the central part retains the name of the Umbilical Region (4). Moreover, the right and left parts of the Hypogastric Region are at the same time each divided into two, which are termed the Iliac Re gions (9, 9), while the central part is termed the Region of the Pubis (5).
The term Abdomen, as applied by entomolo gists to Insects, has a somewhat different signification from the same term when applied to other animals, being used for the whole portion of the body of an insect behind the corselet (thorax), and including the back as well as the belly. It consists, in most cases, of a number of rings without any jointed members for locomotion, and uniformly encloses a portion of the intestines, though sometimes but a very small one.
These rings, or very short hollow cylinders, are severally united with each other by a joint, by a membrane, or sometimes by an intimate junction, the exact line of which is not very apparent. The rings in some cases, as in the grub of the chameleon-fly, slide into one another like the tubes of an opera-glass. Each ring is technically termed a segment (segmentum), virtually composed of two principal pieces, which, when distinct, are termed arches; the upper the arch of the back, the under the arch of the belly. In some cases these two portions are not distinct, but, when they are so, the two borders usually come into contact. When they do not, but remain free, one usually, more or less overlaps the other, as in bees. In caterpillars, grubs, and wingless insects, such as the flea, where the joining of the corselet with the abdomen is not apparent, the abdomen may always be known by the legs never being jointed with it ; and in caterpillars it usually consists of all the body behind the six fore legs, which are always on the corselet.