Morphology and ultrastructure of the pronephros of Testudo hermanni Gmelin, 1789 (chelonian reptiles).

The aim of this study was to investigate the morphology and ultrastructure of the pronephros of Testudo hermanni as observed in the earlier part of its development. This paired structure appears during renal ontogenesis and originates from the first somites localised in the cephalic part of the embryo. The first pronephric evidence is noted at stage 12. The kidney is composed of large glomeruli that are devoid of a capsule and protrude into the coelomic cavity. A ciliated nephrostome provides access to short renal tubules, lined with a well-developed brush border. Two nephric ducts on the lateral sides of the embryo are connected to the tubules. The cytological characteristics of the pronephric structure suggest that it might be functional, at least in the first part of development. The pronephros of Testudo hermanni regresses after a short time around stage 18, while the mesonephros is already well differentiated. Its plesiomorphic characteristics, similar to those observed in amphibians, might be related to the phyletic position of chelonians within the reptiles.