Electron microscopic and histological methods were applied to explore the development and degeneration of mesonephros,and the patterns and characteristics of metanephric development and differentiation.Mesonephros and metanephros were observed at 9 different incubation stages.Results showed that some mesonephric vesicles appeared in the vicinity of the anterior mesonephric ducts at the 16th stage.At the 18th stage mesonephric tubules took shape.At the 26th stage mesonephric tubules' blind ends invaginated,resulting in primitive renal sacs and glomerulus as well as mesonephric tubules elongated distinctly and curved back and forth.All mesonephric tissue had produced integrated nephric units during the 33rd-37th stages.During the 37th-46th stages mesonephric tissue from anterior to posterior of the embryos degenerated in turn.At the 26th stage of incubation,ureteric bud from cloaca grew into metanephrogenic tissue which produced many metanephrogenic vesicles.At the 33rd stage renal tubules and renal sacs appeared and renal tubules lengthened apparently and folded regularly,indicating morphological differentiation of collecting convoluted tubules,proximal convoluted tubules and distal convoluted tubules.During the 37th-46th stages renal corpuscle developed and matured,and renal tubules produced functional differentiation graduall,indicating morphological differentiation the neck part of tubules.Mesonephros of chick embryo had excretory functions.Development and differentiation evidently vary with time changes at different sections of mesonephros.During development and differentiation of nephric units,renal corpuscles in different developing sections appeared at the same stage.The differentiation of collecting convoluted tubules was earlier,which induced the differentiation of proximal and distal convoluted tubules.The differentiation of neck part of tubules occurred later.