[A microdissection study of Lampetra fluviatilis lamprey nephrons].

Each of the nephrons in the lamprey L. fluviatilis consists of three distinct segments-proximal, thin, and distal ones. Proximal segments are differentiated into a convoluted and a descending parts, whereas distal ones-into a convoluted and an ascending parts. Therefore microdissection studies indicate that the anatomical composition of a single nephron in the river lamprey is identical to that of a superficial nephron in mammals. Parallel arrangement of the proximal descending, thin, and distal ascending segments, as well as of the collecting tubules, also makes the kidney of the lamprey similar to the countercurrent system in the medulla of mammalian kidney. The data obtained imply that Henle's loop is present in the kidneys not only of higher Vertebrates, but of Cyclostomes as well.