RENAL FUNCTION 267 



These mechanisms are apparently absent from the kidney and so He out- 

 side the range of this review ; but this group of animals might profitably 

 receive further attention, since this appears to be a very ill-adapted kidney 

 for so remarkable an animal. 



In another marine form, the lobster, evidence for filtration has been 

 accumulated by Burger (1953, 1955a) and has been reviewed above. 

 Burger has established the reabsorption of glucose with evidence parallel 

 to that for the mollusc. A normal animal with a blood-sugar concentration 

 of 24-40 mg.% shows no glucose in the urine. But when exogenous 

 sugar raises the blood-sugar level to 100 mg.%, glucose begins to appear 

 in the urine ; reabsorptive capacity has been exceeded. Under the influence 

 of phlorizin the reabsorptive mechanisms are blocked and glucose appears 

 in the urine without the addition of exogenous glucose. Burger does not 

 state whether, in this last case, the U/B ratio is one, as the filtration 

 hypothesis implies. In the lobster, as in the palaemonids, the regulation of 

 sodium and chloride ions does not appear to be a concern of the renal epi- 

 thelium. Burger finds, however, that the divalent ions of calcium, mag- 

 nesium, and sulfate are concerns of the kidney, though only the calcium 

 appears to be reabsorbed in substantial quantity and this Burger feels is 

 still unproved. 



Annelids 



In some members of this group of animals the problem of reabsorption 

 is increased in complexity by the presence not only of filtering areas but of 

 nephrostomes which can admit not only crystalloids to the epithelial lumen 

 but colloids and formed bodies as well. As an added complexity some of 

 the "open" nephridia drain into the gut, thus allowing for an additional 

 site of reabsorption which might be preceded by a digestive process. We 

 have, too, the added complexity of loss of fluid through the dorsal pores 

 of the terrestrial forms, but quantitative studies of this route of loss are 

 not available. In an earthworm presenting these complexities, Pheretima 

 posthimia, evidences for filtration provided by Bahl (1945, 1947) have 

 already been described. This author found significant evidence for reab- 

 sorption which covers several categories of compounds : proteins, hemo- 

 chromogens, salts, and creatinine. 



The results indicating the reabsorption of protein are not completely 

 convincing. The blood of this species contains about 3.6% protein, a 

 relatively high level, but it may be assumed that the protein of the blood 

 is held back in the filtration process. Coelomic fluid may run into the open 

 nephrostomes with little hindrance but in a quantity which, relative to the 

 blood filtrate, is not known. The protein content of coelomic fluid is much 

 less than that of blood and the urine contains only about 1/16 of the amount 



