THE PHYSIOLOGY OF EXCRETION IN MOLGULA (TUNICATA, ASCIDIACEA)

1. The present contribution includes a review of past work on excretion in Tunicata. 2. In M. manhattensis the single-celled wall of the renal sac absorbs the excretory products, develops the concretions, and discharges them into the cavity of the sac, where they are stored throughout life. 3. The concretions consist of granules, some of which show three or four concentric lamellae caused by further deposition of excretory matter on top of the originally secreted granule. 4. The correlation between body weight, weight of renal sac, and weight of concretions is given. It is shown that accumulation of concretions is not uniformly maintained throughout the life of the tunicate. 5. If the adult renal sac be entirely removed, no regeneration or formation of secondary sacs takes place. 6. The renal fluid is hypertonic to sea water, whereas the body fluid is hypotonic. 7. The molecular concentration of the renal fluid is 3.45 gm./100cc.; of the sea water at Woods Hole 3.10 gm./100 cc.; and of the body fluid 2.75 gm./100 cc., corresponding to NaCl concentrations. 8. The renal concretions contain xanthine, guanine, and uric acid.