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 tank open surface free of rocks or other materials that might damage the walls. A fine layer of sand or a special ground cloth is often used to minimize surface irregularities. Ground cloths are generally made from a geotextile fabric designed to minimize the chance of abrasion and tank failure. Bladder tanks are lightweight, flexible, mobile and can last for many years. The materials used to make bladder walls are recyclable and can be re-used for other purposes. Bladder tanks have capacities up to 1,000 cubic meters. Liquid stored in a flexible bladder tank does not evaporate and any odor it