Key points are not available for this paper at this time.
Evidence is presented for the view that the glomerular development of the kidneys of vertebrates is related to water excretion. The protovertebrate kidney was at one, stage probably aglomerular and the glomerulus was evolved as an adaptation to a fresh-water habitat. In the lower vertebrates remaining in fresh water (dipnoans, ganoids and fresh-water teleosts) and in those still in intimate dependence on it (Amphibia), the glomerular development is good; but with the secondary assumption of a marine habitat (marine teleosts) or with the asumption of terrestrial life in which water conservation becomes a necessity (arid-living reptiles and birds) the glomerular development is extremely poor. In the mammals (and possibly to some extent in lower vertebrates) the primitive water-excreting function of the gbomerulus has been secondarily diverted to a filtration-reabsorption system designed to excrete waste products without the loss from the body of excessive quantities of water. The relative importance of tubular secretion in any kidney will, on this view, depend upon the extent of glomerular development.
Marshall et al. (Wed,) studied this question.