NOTES ON THE BEHAVIOR OF THE FIDDLER CRAB. 195 



is of a definite length. One is sure that the behavior of a Uca 

 is determined by very many different factors. 



4. The question of periodicity in the life of the fiddler crab is 

 a very complicated one, as there are some theoretical objections. 

 In my opinion the problem of intrinsic periodicity of the life 

 phenomena resembles very much the famous problem of the 

 inheritance of acquired characters. The rising tide brings a 

 variety of factors with it and so does the falling tide. The life 

 of a crab is fairly periodic and this is due to an approximative 

 periodicity of external factors. Now If we observe the animal 

 in the laboratory where conditions are fairly constant, there are 

 no factors which in nature cause the rhythmicity of behavior. 

 How could we expect such a rhythmicity? Every kind of 

 activity is a reaction to certain stimuli. The peculiar character 

 of all these reactions is hereditary and fairly constant for each 

 species. But it surely does not mean that in the entire absence 

 of those stimuli the reactions would remain the same. Such a 

 "memory" is an obvious impossibility. If the causes are absent 

 the effect will be absent also. We do not think that under 

 natural conditions the periodicity of behavior of a fiddler is due 

 entirely to the "memory" and not to the periodicity of tides. 

 But only in this case we could expect the animal to behave 

 rhythmically under the constant laboratory conditions. As to 

 the cause of all rhythmicity, the tides, it is interesting to note 

 that they are not rhythmic at all. I quote a random instance 

 from Eldr&ge's Tide-Book for 1925. Successive intervals be- 

 tween the high-tide, low-tide, high-tide, etc., during the ten 

 days are, in minutes: 



349 308 389 3i6 



406 380 360 4 26 



341 356 324 364 



401 399 419 376 



346 312 385 3ii 



410 430 360 431 



353 38i 32i 349 



389 37i 419 390 



344 32i 379 308 



412 421 365 434 



14 



