Having arrived at this general conception of the disposition of the parts of the factory, we may next proceed to consider the machinery of alimentation which is {51} contained within it, and which is represented by the various divisions of the alimentary canal, with its appendages; by the apparatus for the distribution of nutriment; and by two apparatuses for getting rid of those products which are the ultimate result of the working of the whole organism. And here we must trench somewhat upon the province of _Morphology_, as some of these pieces of apparatus are complicated; and their action cannot be comprehended without a certain knowledge of their anatomy. The mouth of the crayfish is a longitudinally elongated, parallel-sided opening, in the integument of the ventral or sternal aspect of the head. Just outside its lateral boundaries, the strong mandibles project, one on each side (fig 3, B; _4_); their broad crushing surfaces, which are turned towards one another, are therefore completely external to the oral cavity. In front, the mouth is overlapped by a wide shield-shaped plate termed the upper lip, or _labrum_ (figs. 3 and 6, _lb_); while, immediately behind the mandibles, there is, on each side, an elongated fleshy lobe, joined with its fellow by the posterior boundary of the mouth. These together constitute the _metastoma_ (fig. 3, B; _mt_), which is sometimes called the lower lip. A short wide gullet, termed the œsophagus (fig. 6, _oe_), leads directly upwards into a spacious bag, the _stomach_, which occupies almost the whole cavity of the head. It is divided by a constriction into a large anterior chamber (_cs_), into the under face of which the {52} gullet opens, and a small posterior chamber (_ps_), from which the intestine (_hg_) proceeds. In a man’s stomach, the opening by which the gullet communicates with the stomach is called the _cardia_, while that which places the stomach in communication with the intestine is named the _pylorus_; and these terms having been transferred from human anatomy to that of the lower animals, the larger moiety of the crayfish’s stomach is called the _cardiac division_, while the smaller is termed the _pyloric division_ of the organ. It must be recollected, however, that, in the crayfish, the so-called cardiac division is that which is actually furthest from the heart, not that which is nearest to it, as in man.