REPORT OF COMMISSIONERS OF INLAND FISHERIES. 143 



consequently furnish an additional confirmation of the principles of 

 secondary' symmetry as formulated by Bateson, 



B. Symmetrical Chela::. 

 Specimens Nos. 6, 8, and 9. 



It seems difficult at present to bring the regeneration of two 

 "crusher" claws in the lobster under any definite principles of reg- 

 ulation or developmental mechanics. 



The phenomenon of two similar "nipper" chelae, indeed, does not 

 seem so remarkable, especially when we take into account the larval 

 development. The adult lobster normally has two distinct types of 

 claws; the more primitive toothed or "nipping" claw, and the larger 

 and phylogenetically younger (according to Stahr, '98, and Przibram, 

 '01) "crushing" claw. But in the larval stages, on the contrary, 

 both are similar and of the nipper type. At about the sixth stage 

 (Hadley, '05) one of these claws begins to differentiate into a 

 " crusher." During ensuing moults this claw passes through transi- 

 tional stages and is finally completely transformed into a crusher 

 claw. It seems very plausible, therefore, that the presence of two 

 similar "nipping" chelae in an adult lobster, as in specimen No. 6, 

 may be accounted for as due to a retarded differentiation during 

 normal development. 



Furthermore, the writer has found in several experiments that 

 when the crushing claw has been autotomously removed, the regen- 

 erated "crusher" is not always distinguishable as such, but may 

 rather present characteristics intermediate or transitional between 

 the more primitive nipping and the more highly developed crushing 

 type (Emmel, '06). If the crusher claw is phylogenetically the 

 younger type, this might, perhaps, be expected, for then this varia- 

 tion in the regenerating structure may be regarded as a reversion 

 to the phylogenetically older or nipping type of claw. We may thus, 

 in another way, again account for a lobster with two "similar nip- 

 ning" chela. 



