The most notable characteristic of these animals is the formation of the stomach, which is divided into several compartments of different construction. The second of these stomach compartments is small and lined with cells of a honey-combed appearance. The slightly chewed food, on reaching this receptacle, is gradually moulded into pellets or small masses, which, instead of passing into the next lower division of the digestive apparatus, rise into the throat, are re-conveyed to the animal’s mouth, and are slowly chewed into a fine pulp. Any one who has watched a cow or sheep lying at ease, calmly and steadily chewing the cud, has seen a picture of quiet enjoyment. The lowest division of the stomach of a cud-chewer is called the rennet-bag, from a fluid called rennet, which it contains, which digests all the food. Rennet has the property of curdling milk, or rather of making it partly solid without rendering it sour. It is used in making cheese. This rennet, mingled with the well-masticated food of the cud-chewers, completes the process of digestion. All liquids swallowed by these animals find their way at once to the rennet-bag. All cud-chewers feed upon vegetable substances, and chiefly upon grass, of which they eat the stalks and fibrous portions as well as the blades. In a former lesson we spoke of the need of sheep for “roughness,” as stock men call it--a need which is shared by all ruminants. This roughness is the coarse and innutritious portions mixed with the richer parts of their food, to enable them to chew the cud, and to prevent indigestion, which would be caused by too rich and compact diet. The teeth of cud-chewers are especially formed for grazing; there are no incisors or cutting teeth on the upper jaw, except in the camel family. The teeth are of two kinds, incisors (on the lower jaw) and grinders, or molars. These grinders are wide teeth, and as the jaws move, the molars act upon each other from side to side, the lower jaw grinding against the upper one. Watch a cow as she eats, and you will observe this motion. Now let us look at these even-toed feet. You will say that these animals have hoofs divided in the centre, while the hoof of a horse is not divided at all. The pig, which does not ruminate, has a hoof centrally divided, like that of a sheep; and the hare, which chews the cud, has several separate toes, and belongs to the rodents. Amid all this diversity there is this constant characteristic, that the cud-chewers of the ungulates have the toes of each foot collected under what is called a cloven hoof, as if a solid hoof had been cleft into two. There are four families of even-toed ruminants--the hollow-horned, including kine, sheep, goats, and antelopes, the deer tribe, the camel tribe, and the camelopards.