title: Ultrastructure of the pronephric kidney of embryos and prolarvae of the sea lamprey, Petromyzon marinus.
abstract: Embryos of lampreys Petromyzon marinus were obtained through a technique of artificial fertilization. Samples of developmental intervals to the prolarval stage were prepared for transmission electron microscopy and the pronephros was examined. The pronephros was visible in the cardiac region of the coelom prior to the time of hatching of embryos and consisted of a renal corpuscle, nephrostomes, and proximal tubules connected to a pronephric duct. The renal corpuscle was comprised of poorly-defined vascular channels and a visceral epithelium of yolk-filled cells, the podocytes, with short major processes and pedicels resting on a basal lamina. The first proximal tubules possessed a delicate brush border of short microvilli but subsequent cellular differentiation yielded cells with all the components required for the process of endocytosis, a process which was demonstrated by uptake of the tracer, horseradish peroxidase. The distal tubules appeared later in development and were noted for abundant mitochondria and an extensive smooth tubular network. The timing of differentiation of various components of the nephron corresponds to that seen during morphogenesis of other vertebrate kidneys.
authors.affiliation: Department of Anatomy, University of Toronto, Toronto, Ontario, Canada, M1C 1A4; Department of Scarborough Campus, University of Toronto, Toronto, Ontario, Canada, M1C 1A4.
authors.forename: L C
authors.initials: LC
authors.lastname: Ellis
authors.forename: J H
authors.initials: JH
authors.lastname: Youson