Having worked over the Cockroach from the outside, it will be advantageous to get some acquaintance with its internal anatomy. This is not a difficult matter. The specimen is to be pinned down, under water, with its back uppermost. The wings having been removed, a longitudinal cut is to be made down the centre from the posterior part of the abdomen to the back of the head, and the two sides of the integument turned back. Or the junction between the upper and lower plates on each side may be cut through with a cutting needle, and the whole integument removed. The first task is to clear away the fat-body, a whitish substance which overlies the chief organs of the body. When this is picked to pieces and floated off the digestive system will be exposed. After this has been worked over a few times there should be no difficulty in dealing with similar parts in other Insects. At the back of the head lies the gullet or oesophagus leading into the crop (_c_), at the base of which lies the gizzard (_g_). The interior of this organ is furnished with six strong chitinous teeth, with small ridges of the same substance between them. Towards the posterior end are six cushions, all set with fine bristles. Behind this comes the stomach (_v_), into which open seven or eight tubes, closed at one end, and between it are the Malpighian tubes, which are concerned in the process of excretion. The small intestine (_co_) succeeds, and behind this is the rectum (_r_). [Illustration: FIG. 35.--Alimentary Canal of Cockroach.] It will be interesting to separate the gizzard from the crop (_c_) and stomach (_v_) and break it open with a couple of needles, so as to examine the teeth, which will be more easily made out if the opened organ be allowed to soak for a time in a solution of caustic potash. Similar teeth-like processes are found in the gizzards of many other Insects, and their presence has given rise to some strange ideas. Swammerdam[20] says, ‘I preserve also the threefold stomach of a locust, which is very like the stomach of animals that chew the cud, and particularly has that part of the stomach called Echinus[21] very distinctly visible. I do not, therefore, doubt but locusts chew the cud, as well as the animals just mentioned. Indeed, I persuade myself that I have seen this.’ Somewhat similar teeth-like processes exist in the Lobster, the Crab, and the Crayfish. ‘Professor Plateau has expressed a strong opinion that neither in the stomach of Crustacea nor in the gizzard of Insects have the so-called teeth any masticatory character.’ He adopts Swammerdam’s comparison, but considers them strainers, not dividers of the food[22].