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 group. Increasing fluid intake can facilitate the passage of small bladder stones. However, larger stones may require other methods of treatment. Fragmentation of bladder stones can be achieved by use of a cystoscope which is inserted into the bladder. The urologist visualizes the stone and uses ultrasonic energy or laser lithotripsy to cause fragmentation of the stones into small pieces, which are then flushed out of the bladder. This procedure requires anesthesia and may require admission to a hospital. Complications of this treatment include infection and damage to the bladder. Some stones are too large even for cystoscopic treatment and