Calculi are well known in the renal system of the domesticated animals so that it is not surprising to find them well represented all through the lower orders. Their structure, composition and effects do not differ, however, and it remains only to point out their distribution. One of the frequent results of renal and pelvic lithiasis is, however, missing in our records, namely hydronephrosis, and indeed a pressure dilatation of the ureter and pelvis has not been observed in all our experience. This would seem to be explained first upon the infrequency of stone, of obstructive new growths and inflammatory strictures and second by the fact that lower animals do not long survive conditions which would occasion back pressure upon the kidneys. Definite renal and pelvic calculi have occurred in five Ungulata, one each in Edentata and Steganopodes. To these might be added cases of uratic sand in one Carnivora, one Marsupialia, and uratic stones of large size in the cloaca of two Passeres and one Accipitres. Uratic collections within the avian kidney have been mentioned and will be discussed later. According to written descriptions and three preserved examples the calculi in four of the ungulates are mixed urates and carbonates, although one in a deer was said to be “mulberry” in surface. The specimens at hand are moderately hard with rough irregularly crystallized outer shells like carbonate deposits. Incomplete moulding to the calyx is found. The pelvic cavity while seeming to be enlarged is not distended nor do the stones assume the “antler” character and distort the pyramid. All the animals showing these stones have but a single pyramid in the kidney. The fifth example in the ungulate had early stones forming in the apex of the pyramid and not yet discharged into the pelvis. Four of these cases showed stones on both sides, one only in the left kidney. The case among the Edentata concerned an Armadillo (_Tatu novemcinctus_), in the kidney of which there were definite smooth, round, hard pebbles in the right pyramid and several fine grains in the pelvis. There was a recent hemorrhage in the pelvis which, from local appearances and autopsy survey, was due to the lithiasis. A Gannet (_Sula bassana_) represents the only avian true calculus. In this case many small, hard, yellow stones occupied the right pelves, which contained also loose urates. The lobules were much distorted and showed a mild interstitial change. This accumulation was confined to the left side. These well developed cases having been mentioned the next most important may be quoted: