. The biology of marine animals. Marine animals; Physiology, Comparative. EXCRETION 297 physiology of nephridia in lower animals, and any role that they may have in voiding nitrogenous excreta still awaits quantitative analysis. Other suggested functions are osmoregulation and ionic regulation, and in the earthworm it has been discovered that a urine is secreted which is strongly hypotonic to the body fluids (42). In marine gastropods and lamellibranchs ammonia is an important constituent of nitrogen excretion, but various species, notably Mytilus, have an appreciable amino-acid fraction (Tabl
. The biology of marine animals. Marine animals; Physiology, Comparative. EXCRETION 297 physiology of nephridia in lower animals, and any role that they may have in voiding nitrogenous excreta still awaits quantitative analysis. Other suggested functions are osmoregulation and ionic regulation, and in the earthworm it has been discovered that a urine is secreted which is strongly hypotonic to the body fluids (42). In marine gastropods and lamellibranchs ammonia is an important constituent of nitrogen excretion, but various species, notably Mytilus, have an appreciable amino-acid fraction (Table ). No urine analyses are. Vent rat lip Nephridiopore Body wall Fig. Excretory Ducts of Worms (a) Typical solenocyte of a polychaete; (b) inner end of a nephridial canal of a polyclad turbellarian, with flame cell at extremity; (c) metanephromixium of Odontosyllis. Dorsal and ventral lips pertain to the nephridiostome. (From Goodrich.) available but it seems likely that some fraction of the total excretory-N is discharged in the urine. There is evidence that fluid is filtered across the heart wall into the pericardium and then enters the kidneys. By producing a urine hypotonic to the blood the kidneys of freshwater species participate in the maintenance of a hyperosmotic internal milieu. The total output of non-protein nitrogen in a medium-sized octopus amounts to about 25 mg/day. Half of this is ammonia, but there are ap- preciable amounts of urea and amines, amounting to 15 and 20% res- pectively. Since the data are not related to body weight, it is impossible to partition nitrogen excretion by renal and extrarenal routes. The urine —10*. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Nicol, J. A. Colin (Joseph Arthur Colin), 1915-. New York, Interscience Publishers
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