The kidney of the ox (Pl. IX, fig. 1) is a compound organ made up of 15 to 25 separate lobules like so many separate kidneys, but all pouring their secretion into one common pouch (pelvis) situated in an excavation in the center of the lower surface. While the ox is the only domesticated quadruped which maintains this divided condition of the kidney after birth, this condition is common to all while at an early stage of development in the womb. The cluster of lobules making up a single kidney forms an ovoid mass flattened from above downward, and extending from the last rib backward beneath the loins and to one side of the solid chain of the backbone. The right is more firmly attached to the loins and extends farther backward than the left. Deeply covered in a mass of suet, each kidney has a strong outer, white, fibrous covering, and inside this two successive layers of kidney substance, of which the outer is that in which the urine is mainly separated from the blood and poured into the fine, microscopic urinary ducts. (Pl. X, fig. 1) These latter, together with blood vessels, lymph vessels, and nerves, make up the second, or internal, layer. The outer layer is mainly composed of minute globular clusters of microscopic, intercommunicating blood vessels (Malpighian bodies), each of which is furnished with a fibrous capsule that is nothing else than the dilated commencement of a urine tube. These practically microscopic tubes follow at first a winding course through the outer layer (Ferrein's tubes), then form a long loop (doubling on itself) in the inner layer (Henle's loop), and finally pass back through the inner layer (Bellini's tubes) to open through a conical process into the common pouch (pelvis) on the lower surface of the organ. (Pl. X, figs. 1, 2, 3.)