Dialysis blocks the passage of larger substances (for example, red blood cells, large proteins). This replicates the filtering process that takes place in the kidneys when the blood enters the kidneys and the larger substances are separated from the smaller ones in the glomerulus. The two main types of dialysis, hemodialysis and peritoneal dialysis, remove wastes and excess water from the blood in different ways. Hemodialysis removes wastes and water by circulating blood outside the body through an external filter, called a dialyzer, that contains a semipermeable membrane. The blood flows in one direction and the dialysate flows in the opposite.
Bidder's organ oocytes (egg cells). Only rudimentary oviducts are developed, though, preventing eggs from actually being laid. The Bidder's organ only develops into an ovary analogue when testes are removed experimentally or not functioning properly (e.g. due to exposure to endocrine-disrupting chemicals). Importantly, females can have Bidder's organs in addition to true ovaries, which suggests that the Bidder's organ might not be a rudimentary ovary. It is named in honour of Friedrich Bidder. The organ's internal anatomy consists of two parts; the central portion, consisting of connective tissue and rich in blood vessels, and its periphery, consisting of the cortex, which contains