Studies of the embryonic development of primitive vertebrates, such as the dogfish , clearly show that the excretory system arises from a series of tubules, one pair in every segment of the body. This continuous series of tubules constitutes the archinephros, the name implying that the kidney of the ancestral vertebrate had some such form as this. Each tubule opens internally to the body cavity and may, in the remote past, have opened separately to the exterior; but in all living vertebrates the tubules open on each side into a longitudinal duct, the archinephric duct. At the posterior end of the body cavity the two archinephric ducts unite before opening to the exterior. Later in development, Bowman’s capsule arises as a diverticulum of each tubule, subsequently becoming indented by the glomerulus.
24 сен 2024
