REVERSAL OF ASYMMETRY IX ALPHEUS. 2OQ 



sents, in its main features, the completion of a process that is 

 inhibited or held in abeyance in the normal condition ; though in 

 the male this forward movement is accompanied by a regressive 

 process which causes the disappearance of its specific modifications 

 (setose ridge of the dactylus). To vary the statement, the 

 development of Alpheus, at first symmetrical, tends towards 

 a state of equilibrium, characteristic of the species, which is 

 attained through a great inequality in the size of the two chelae 

 and a series of structural modifications affecting especially the 

 larger one. With the removal of the larger chela the normal 

 equilibrium is reversed and the restorative process proceeds on 

 both sides along the same general lines as in the normal develop- 

 ment until a condition of normal equilibrium is restored. A 

 similar interpretation will perhaps apply to Brachyura examined 

 in Przibram's second interesting communication,' where it is 

 shown that after the removal of either or both chelae the reeen- 



O 



crated form is always that of the less modified form (which is 

 usually also the smaller). Where only the crushing chela is 

 removed the remaining chela is not transformed into one of the 

 other type ; hence no reversal occurs. This case is clearly 

 intermediate between that of Alpliens, in which complete reversal 

 occurs, and Homants, in which, as Przibram shows, no reversal 

 occurs, each chela regenerating one of its own type whether one 

 or both is removed. The Brachyura in question (Carcinus, 

 Portunns, Eriphid) exhibit one element of the reversal, namely, 

 the formation of a less modified chela from the stump of the 

 crushing-chela ; but fail to complete the metamorphosis of the, 

 remaining one. This may be due either to the slowness of the 

 process (which may require a longer time for its completion than 

 that during which the animals were kept under observation) or 

 to a greater rigidity of organization. In Homarns the regener- 

 ating crushing claw is not in its very early stages recognizable 

 as such, but is of the embryonic type ; it assumes many of its 

 characteristic features very early, but for a long period remains 

 of a type intermediate between the two forms of chelae (cf. Przi- 

 bram's Figs. 13, 14). No reversal occurs. These various cases 



1 " Experimentelle Studien iiber Regeneration," II.; Arch. Entwkm., XIII., 

 1901-02. 



