HABITS OF FIDDLER CKABS — PEAKSE. 427 



might be interpreted as manifestations of a desire to play. The in- 

 stinct to fight males of his own species and size is very strong in a 

 fiddler, yet this instinct is more than a " fighting reflex," for he is 

 slow to resent an attack by a smaller male. 



Concerning the structural differences between the sexes, it may be 

 affirmed that the great chela of the male does not serve for burrow- 

 ing or feeding. In fact, it is rather a disadvantage in either of these 

 activities. The great chela closes the burrow inasmuch as it fills the 

 opening as a weapon of offense, but is not used as a lid or stopper. 

 It is of no advantage during actual mating, but unquestionably 

 serves as a signal which is waved to attract the attention of females. 

 The great chela is of undoubted use to the male in 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 the tusks of 

 the walrus. Among higher animals in which the males possess such 

 aggressive organs, however, the females are protected and cared for 

 to some extent, but nothing of this sort is known among decapod 

 crustaceans with secondary sexual adaptations {Uca, Alpheus, and 

 others). Thus, although many of the Crustacea have two adaptations 

 which might fit them for colonial life — through the mother carrying 

 her eggs and young for a time, thus having opportunity to start a 

 colony with them, and through the aggressive adaptations of the 

 males, which might enable stronger individuals of that sex to gather 

 a number of females about them — their instincts have prevented 

 them from developing it. 



Alcock (1892) believes "no one can doubt that the claw of a male 

 has become conspicuous and beautiful in order to attract the female," 

 and that " it is used as a signal to charm and allure the females." 

 Though there are perhaps such minor objections to such a statement 

 of the case, it is certain that male fiddlers do wave their claws, dance, 

 and pose in the presence of females. It must be admitted, also," that, 

 though bright colors occur on other parts of the bodies of both sexes, 

 the great chela are always colored so that it is conspicuous. At pres- 

 ent it is not possible to state just what part specific colors may 

 play in attracting the females of particular species. The problem 

 should be studied during the active mating season with special refer- 

 ence to color. By observing the coloration of males actually chosen, 

 by painting the chelae of rejected suitors, by " waving " colored mock 

 chelae, or by other tests, a definite conclusion could doubtless be 

 reached. Until such experiments have been made it can hardlj^ be 

 affirmed that fiddler crabs show the operation of sexual selection 

 through color discrimination. 



