192 JAX B. DEMBOWSKI. 



air-chamber at the bottom of the burrow seems to support this 

 view. It is probable in fact that the crab under its natural 

 conditions practically is never out of the air. I kept several 

 tiddlers in a jar the bottom of which was covered with a very 

 thin layer of moist sand (2-3 mm.). The jar was covered and 

 thus the atmosphere within it was saturated with vapor. The 

 gill-chamber was prevented from drying but at the same time 

 there was no chance of changing its liquid. Under such con- 

 ditions the crabs lived very well for over 6 weeks and would 

 probably have lived much longer had I not broken the experiment 

 up. I failed to find anywhere data as to how long a fiddler may 

 live under the water. Schwartz and Safir mention only that 

 probably the fiddlers "do not find prolonged submergence very 

 comfortable" (15, p. 19). And yet my fiddlers lived under the 

 water for 6 weeks without showing any abnormalities and are 

 still alive. To the end of this time they move rapidly when 

 frightened and feed on mussels under the water. It is clearly to 

 be seen that the flagella make their rhythmic movements, which 

 in all crabs serve for renewing water in the gill-chamber. So 

 the fiddler crabs seem to be true water-breathing forms like all 

 other crabs. But at the same time the contents of their gill 

 chamber may be thoroughly ventilated in the air. It does not 

 mean that they breathe air, nevertheless such a wide scale of 

 adaptation furnishes an interesting example. The last experi- 

 ment does not support the opinion of Abbott that the liquid of 

 the gill-chambers has a lower osmotic pressure as compared 

 with the sea water. It seems to me rather that this liquid 

 cannot be anything else than the pure sea water. 



3. A further question arises: why is the burrow of a fairly 

 definite length, or, what conditions cause the crab to stop its 

 working? There are several possibilities which may be tested 

 experimentally. 



The crab may stop after having expended a certain amount 

 of energy in digging. But the resistance of the ground may be 

 very different depending on the degree of moisture, presence of 

 mud, small stones, plant roots, etc. The amount of spent 

 energy may be very different in every single case and yet there 

 is no evidence that the length of the burrow is affected by those 



