Functional aspects of renal glomeruli based on scanning electron microscopy of corrosion casts, with special emphasis on reptiles and birds.

The glomerular complexity of several species of birds and reptiles is investigated in this study by scanning electron microscopy of vascular corrosion casts. Comparing these results with those of a freshwater teleost and a mammalian species, a trend towards small, simple glomeruli of the avian type, beginning with large, well vascularized glomeruli resembling the type found in fish, can be observed in reptiles. A close correlation between glomerular size and habitat can be established comparing related species having a similar physiological mode of renal function. Entirely different from this sauropsidian evolutionary line of development is the highly complex, large differentiation of the mammalian glomerulus.