170 J- F. ABBOTT. 



director of the laboratory, he is under especial obligation for the 

 constant courtesy and generous assistance of which he was at 

 all times the recipient. The present paper deals only with the 

 effect of pure distilled water upon the fiddler crab. 



The crabs inhabit burrows in the sandy or marshy shores, the 

 openings of which are usually, though not always, covered by 

 the tide. At high tide the crabs retreat to their holes which they 

 plug up with sand. As the tide ebbs they emerge and begin 

 feeding, frequently going a considerable distance from their holes. 

 In the interval between high tides, if the sun is bright and the day 

 hot the males go through characteristic and energetic "dances." 

 Altogether they spend many hours of vigorous activity out of 

 the water. A related genus of the same family, Ocypoda, lives 

 out of the water almost entirely and spends most of its time 

 running about on the dry sand. 1 In accordance with this habit 

 a peculiar modification has developed in connection with the gill 

 chambers. In these two genera these are very large and cavern- 

 ous, the two chambers together equalling approximately the 

 space occupied by the viscera. The gills lie in the floor and the 

 large space above them is normally filled with liquid. Com- 

 municating with this chamber, in addition to the ordinary 

 openings for the exit and entrance of water, there is an aperture 

 between the basal joints of the third and fourth legs, bounded 

 by chitinized lips which bear tufts of hairs. This opening 

 communicates between the cavity above the gills and the exterior 

 by a sort of canal provided with a ciliated valve. By means of 

 this arrangement, not only is the animal able to store up a large 

 amount of water above the gills but it is also possible for a 

 constant gaseous exchange to take place between this contained 

 water and the air without. In other words the crab when out 

 of the water is able to breathe air. 



This accounts for the apparent tolerance of the animal to 

 pure distilled water. When immersed in distilled water it feeds 

 out through this channel some of the sea water contained in its 

 gill chambers. As with some other Crustacea a very small 

 amount of NaCl in the surrounding medium is sufficient to 

 preserve the integrity of the membranes and permit the animal 



1 Cf. Cowles. Carnegie Inst. Papers, Tortugas Lab., II., 1908. 



