EFFECT OF DISTILLED WATER UPON THE FIDDLER CRAB. iyi 



to live in spite of the greatly altered osmotic pressure. That 

 the crab accommodates itself in this way was shown by the 

 following experiment. Five crabs that had been running about 

 in a dry tank for a week were rinsed off in running fresh water, 

 dried, and immersed in 250 c.c. of pure distilled water which was 

 removed and renewed at short intervals. These samples were 

 then titrated for chlorides by the Volhard method with the 

 following results: 1 



Interval of Immersion in 

 Pure Distilled Water. Cl in Milligrams. 



30 minutes 0.038 



1 hour 0.188 



2 hours 0.263 



3 hours 0.132 



3! hours 0.297 



Total Cl 0.918 



The crabs were moribund in another half hour. The gill 

 chamber capacity of each crab was roughly Y^ c.c. The per- 

 centage of Cl in Beaufort sea water is 1.963 gm. per 100 or .049 

 gm. to 2^2 c.c. The detectible salinity emitted by the crabs 

 was thus only about 20 per cent, of that of sea water. Some 

 may have been "held back," but it is more probable not only 

 that the crabs in the experiment, which had been out of water 

 for a week, but also crabs running about out of the water nor- 

 mally have their gills bathed by a liquid of only about one fifth the 

 concentration of sea water. Experiment has shown that they 

 will live indefinitely when immersed in very much greater 

 dilutions, although I have not found that they will endure such 

 a dilution as that used by Bullot 2 for fresh-water Gammarus 

 (o. 00008 TV). 



In subsequent experiments the side of the gill chamber was 

 cut away and the contents rinsed out with distilled water so 

 that not only were all salts washed away but the gills were 

 directly exposed to the action of the medium. Even under such 

 circumstances the crab does not at once die when placed in 

 distilled water but will live actively usually from four to six 



1 For assistance in carrying out this portion of the experiments as well as for 

 many helpful suggestions the writer is indebted to Mr. Wm. J. Crozier. 

 1 Univ. of Calif. Pub. Physiol., 1904, Vol. I., p. 199. 



