Kidney always so simple; in cartilaginous fish and some amphibians, there is also a shorter duct, similar to the amniote ureter, which drains the posterior (metanephric) parts of the kidney, and joins with the archinephric duct at the bladder or cloaca. Indeed, in many cartilaginous fish, the anterior portion of the kidney may degenerate or cease to function altogether in the adult. In the most primitive vertebrates, the hagfish and lampreys, the kidney is unusually simple: it consists of a row of nephrons, each emptying directly into the archinephric duct. Invertebrates may possess excretory organs that are sometimes referred to as
Bladder stone and extract bladder stones. Celsus gave the first description of lithotomy as performed before and during his time, and the operation has ever since borne his name—the Celsian method. Lithiasis (stone formation) in the bladder is called cystolithiasis (), from "cysto-" (bladder/cyst) + "-lith" (stone) + "-iasis" (disorder). Bladder stone A bladder stone is a stone found in the urinary bladder. Bladder stones are small mineral deposits that can form in the bladder. In most cases bladder stones develop when the urine becomes very concentrated or when one is dehydrated. This allows for minerals, such as calcium or magnesium salts,