130 PEARSE. 



diurnal habits, and they escape the fishes and snakes that hunt 

 at the edge of the advancing tide by closing the openings of their 

 burrows when the water threatens to inundate them. 



Although the majority of the reactions of fiddler-crabs are 

 stereotyped and appear to be instinctive, yet they are open to 

 some modification. The daily life of a fiddler is more or less 

 of a routine — to dig a burrow, to seek food as long as the 

 territory about his burrow is clear, to attack small aggressors, 

 to retreat from large enemies, to plug the burrow when the tide 

 comes in, to open it when the water recedes, to retire during 

 darkness, and to mate at the proper season. These are his 

 ordinary activities and they depend largely upon unvaried reac- 

 tions. Some instincts are so strong that, although usually ad- 

 vantageous, they may be harmful ; for example, place association 

 and instinct to retire into her hole was strong enough to cause 

 a crab to remain for some time in danger when the burrow 

 could not be entered and she might have escaped by running 

 away (p. 120). Nevertheless, a fiddler shows some ability to 

 modify his reactions to suit circumstances; such as departing 

 from his usual method of carrying mud from his burrow (p. 117) , 

 using different ways to plug the burrow (p. 118), and in some 

 other activities. 



A fiddler-crab is able to establish a place association for a 

 certain locality, and to retain it for as long as three weeks 

 (p. 121). Some activities (p. 125) might be interpreted as 

 manifestations of a desire to play. The instinct to fight males 

 of his own species and size is very strong in a fiddler, yet this 

 instinct is more than a "fighting refiex," for he is slow to resent 

 an attack by a smaller male (p. 123) . 



Concerning the structural differences between the sexes, it 

 may be affirmed that the great chela of the male was not 

 developed for burrowing or feeding, because he never uses it 

 for either purpose ; in fact, it is rather a disadvantage in either 

 of these activities. The great chela closes the burrow inas- 

 much as it fills the opening as a weapon of offense (fig. 5) , but 

 is not used as a lid or stopper. It may be of some advantage in 

 copulation, but this can not be affirmed until someone has ac- 

 tually seen the phenomenon. The great chela is of unquestion- 

 able use to the male in his combats with his fellows and in 

 defending himself from other enemies. In this respect it is 

 comparable to the secondary sexual characters of some other 

 male animals, such as the stag's antlers, the cock's spurs, and 



