THE GENERAL FORM OF EXCRETION IN THE LOBSTER, HOMARUS

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Abstract
A method was found for the repeated evacuation of nephridial bladders. Experimental analysis showed the nephridia capable of concentrating phenol red, para-aminohippurate (PAH), Mg, and sulfate. At normal blood levels glucose and inorganic phosphate are excluded from the urine. The secretory or exclusion powers of the nephridia are swamped by artificially high blood levels. Nephridia are indifferent to inulin, bromsulfalein, elasmobranch hemoglobin and plasma protein, sodium, and chloride. Exogenous urea is lost through the gills. The gills are relatively impermeable to magnesium, sulphate, phenol red but permeable to water and NaCl. A variety of chemical measurements for sea water, blood, and urine were made. In sea water, the distribution of NaCl between sea water, blood, and urine seems to be passive. In dilute sea water, blood chloride is elevated, presumably by some active process in the gills. Urinary chloride is lost at the elevated blood levels indicating a lack of nephridial ability to actively handle chloride. Living lobsters may be completely anuric, but the so-called normal urine flow is about 1 ml/hour/0.5 kg. Anuric lobsters can be converted into normal urinators by the transfusion of blood. While water and NaCl enter largely through the gills, multi-valent ions and organic molecules enter through the gut. The lobster drinks sea water with its food and also intermittently on an empty stomach. This water is absorbed. The volume of the sea water drunk is however, insufficient to account for the volume of urine. For various substances, the nephridia and the gills have individual properties. The nephridia depend on high urine flows rather than on high secretion.