14 
Proceedings of the Royal Society of Edinburgh. [Sess. 
IV. — Period of Survival of the Shore-Crab (Carcinus maenas) in 
Distilled Water. By Robert K. S. Lim. (From the Labora- 
tory of Physiology, Edinburgh University.) Communicated by 
Professor Sir E. A. Schafer, F.R.S. 
(MS. received July 24, 1917. Read November 5, 1917.) 
In some recent experiments on Ligia oceanica, Tait (13) found the period 
of survival of the animals in fresh water to be largely dependent on 
their moult-age, freshly moulted animals surviving longer than animals 
approaching new moult. It was of interest to know whether this result 
applies only to Ligia. At the suggestion of Dr Tait, to whom I am 
indebted for advice and encouragement, I have carried out somewhat 
similar experiments on Carcinus mcenas (Pennant). That this crab does 
survive for an appreciable period in fresh water was first noted by 
Couch (3). At a later period, Plateau (10) showed that newly moulted 
Carcini (and other marine Crustacea) succumbed earlier than the others ; 
that survival varied directly with size ; and that loss of salts, principally 
NaCl, caused the death of the animal. It was only after the present 
experiments had been completed that I learned of Plateau’s paper, so 
that my results are mainly confirmatory. 
Details of Technique. 
The experiments took place during the months of July, August, and 
September 1916, with the room temperature varying from 18° to 21° C. 
The freshly caught crabs were kept without food under damp sea- 
weed in a covered tank. Under such conditions they may survive for 
weeks ; the animals used for experiment, however, were never kept 
longer than four days. The weight is more rapidly determined when 
they are in a semi-dry condition, for in spite of all manipulation a 
variable amount of water adheres to the gills and setae of crabs taken 
straight from sea-water. 
The immersion fluids consisted, in a few experiments, of tap-water, 
but in the others of distilled water. In tap-water the crabs survived, if 
anything, appreciably longer than in distilled water. 
During each experiment the immersion fluid was kept aerated, the 
apparatus for the purpose being the same as that employed by Tait, 
with these two points of difference : viz. that it was found necessary to 
protect each capillary aeration tube with another tube of stout glass, and 
