GENERAL HISTOLOGY

Detailed explanation-1: -In general, fish form the first 2 kidneys, called the pronephros and mesonephros, with the latter being the permanent adult kidney (mammals develop a third kidney, the metanephros, as their final adult kidney).

Detailed explanation-2: -Each kidney is comprised of a fibrous outer layer called the renal capsule, a peripheral layer called the cortex, and an inner layer called the medulla. The medulla is arranged in multiple pyramidal structures that together with overlying cortex comprise a renal lobe (red box).