ABSTRACT
The mean osmolar concentration (expressed as mM. NaCl/l.) of the serum for Lampetra planeri was found to be no mM. in the ammocoete and 113 mM. in the adult. For adult L. fiuviatilis szerum in November the mean osmolar concentration was 143 mM. and in March 136 mM.
In adult planeri the Cl concentration of the body fluids accounted for nearly 90% of the total concentration as compared with only 58% in the serum of the ammocoete. Adult fiuviatilis kept in tap water throughout the winter appeared to show an increase in Cl levels.
Evidence has been produced to support the view that the differences observed in water, fat and Cl content of ammocoete and adult planeri and adult fiuviatilis are consequences of the period of starvation preceding sexual maturity.
Pronounced seasonal variations have been found in the fat and Cl content of ammocoetes of planeri.
The osmotic uptake of water has been determined for adults of both species in fresh water. In planeri the rate of uptake for unit body weight is about four times as great as in fiuviatilis.
Observations have also been made on the osmotic loss of water of ammocoete and adult planeri and of adult fiuviatilis in sea water of different concentrations. For unit body weight osmotic loss of water in planeri is about twice that of fiuviatilis.
Total losses of Cl have been determined for ammocoete and adult planeri in distilled water and their effects on internal Cl levels have been studied. Observations have also been made on the active uptake of Cl.
Acclimatization experiments on ammocoetes and adult planeri and on adult fiuviatilis have failed to produce any evidence of regulation in sea water.
