The renal corpuscle of the opisthonephric kidney of the Great Lakes lamprey, Petromyzon marinus L., is described. In the larvae (ammocoetes) several renal corpuscles, each consisting of lobed glomeruli and Bowman's capsules, are placed behind one another and there is a progressive lengthening of the posterior corpuscles as the animal ages, apparently by the addition of new glomeruli posteriorly. Bowman's capsule surrounds a single loop and consists of parietal and visceral layers which are similar to those seen in higher vertebrates.

The kidney of the adult has a single complex renal corpuscle which extends almost its entire length. Present evidence indicates that the adult kidney is formed during transformation and that the larval renal corpuscles do not contribute to the single elongate corpuscle of the adult. A large number of lobed glomeruli, lying one behind the other, form the elongate glomus. Interposed between each pair of lobes is the dilated end of a nephron. There are no typical Bowman's capsules in the adult although where these nephric capsules invest the blood vessels of a lobe they develop podocytes similar to those of the visceral layer of Bowman's capsule and elsewhere they consist of a simple squamous epithelium similar to that of the parietal layer.