244 CHAkLES R. STOCKARD. 



chela shows characteristic sexual differences, we shall be mainly 

 concerned, however, with the fact that the small chela is always 

 typically different from the large chela in shape as well as in size. 



Przibram 1 discovered that in several species of Alpheus after 

 the removal of the large chela a chela of the small type regener- 

 ated from its base while the small chela of the opposite side meta- 

 morphosed or developed into a great chela of typical form at the 

 following moult. In other words, the asymmetry was reversed. 

 Further, when both first chelae are removed they regenerate in 

 their original conditions, no reversal following. 



Zeleny 2 found an exactly similar phenomenon to occur after 

 removal of the functional operculum in the worm, Hydroides. 

 In this case the rudimentary operculum of the opposite side de- 

 velops into a functional operculum while a rudimentary organ 

 regenerated from the base of the former functional one. The 

 principle involved in this reversal phenomenon is doubtless the 

 same as that in the Crustacea. 



Przibram 3 later found a similar reversal to occur in other 

 species of Crustacea, while in others the removal of either chela 

 is followed by the regeneration of one of the simpler or smaller 

 type without a regulatory change taking place in the uninjured 

 chela of the other side. In still other cases, as for example the 

 lobster, Homorus, a chela similar to the one removed invariably 

 regenerates whether the original chela was a large crusher claw 

 or the slender nipping claw. 



The Crustacea thus present a series from those forms which 

 regenerate appendages of the type of the ones removed, others 

 which regenerate appendages of the simpler type without a com- 

 pensatory change taking place in the uninjured chela, and finally 

 such forms as Alpheus in which (lie simpler type of chela is re- 

 generated after the removal of the more specialized chela while 

 the uninjured small chela develops into the more modified type, 



'Przibram, H., "Experimentelle Studien uber Regeneration," Arch, fur Entw.- 

 Mech.. XI., 1901. 



2 Zeleny, C., "A Case of Compensatory Regeneration in the Regeneration of 

 Hydroides dianthus," Arch. fur. Entw.-Mech., XIII.. 4, 1902. 



"Przibram, H., "Experimentelle Studien uber Regeneration, II.," Arch, fur 

 Entw.-Mech., XIII., 1901-1902; "Equilibrium of Animal Form," Jour. Exp. Zoo/., 

 V., p. 259, 1907-1908. 



