ABSTRACT
The blood of the diamondback terrapin going from fresh water to 50% sea water shows an increase in its osmotic pressure which is mainly due to an increase in Na and Cl concentrations.
The blood of terrapins living in sea water compared with the blood of terrapins living in 50 % sea water shows a higher osmotic pressure which is the result solely of a higher urea concentration; Na and Cl concentrations are no longer affected in this second stage of adaptation.
Urine of 50% sea-water terrapins and of sea-water terrapins is generally isosmotic to the blood while the urine of fresh-water terrapins is usually hypo-osmotic.
The bladder appears to play an essential part in reducing water loss in the seawater terrapins but is not implicated in the salt balance.
When each animal is considered individually, the urea concentration in the urine is always higher than in the serum, suggesting that the high urea concentration in the blood of terrapins adapted to sea water is due to an urea accumulation in the bladder.
Water loss occurs in the first 3 days after transfer from 50 % sea water to fresh water, and the animal suffers general oedema after transfer in the reverse direction. The same changes are also seen in the water content of the muscle joining humerus to clavicle; however, after 11 days of adaptation the water content of that muscle is restored to its usual value of 80 %.
