86 



SCIENCE 



[N. S. Vol. XXVI. No. 655 



such experimental proof, and estdhlish the 

 fact that the process of regeneration is an 

 important factor in the origin of the sym- 

 metrical chelce occasionally found in the 

 adult leister. 



At present it seems diiBcult to bring these 

 cases which show the regeneration of two 

 crusher claws under any definite principles of 

 regulation or a developmental mechanics. 

 Evidently they can not be explained as due to 

 a retardation in the process of ontogenetic 

 differentiation, nor does it appear that they 

 can be regarded as a reversion to a phylo- 

 genetically older type of chelae. It is appar- 

 ently impossible to interpret such a regenera- 

 tion as a case of " compensatory regulation " 

 in Zeleny's" sense, for the regenerated chelse 

 are almost identically similar in size and 

 form. Nor is it clear that they both can be 

 brought under the category of " reversal " phe- 

 nomena, if by this term we mean a reversed 

 order of asymmetry. At present, therefore, 

 these eases must rather be described merely 

 as the substitution by regeneration of the 

 crusher claw in place of an original nipper 

 chela. 



II. The Ontogenetic Origin of Normal Asym- 

 metry. 



The niain question here is, whether normal 

 asymmetry is congenital and wholly prede- 

 termined in the egg, or whether it may be 

 influenced by external factors during develop- 

 ment. 



With regard to this matter Herrick," on the 

 basis of his experiments with the shrimp 

 Alpheus, concludes that asymmetry in the 

 lobster " is probably one of direct inheritance, 

 all members of a brood being either right- or 

 left-handed. That is to say, the normal posi- 

 tion of the toothed or crushing claw is not 

 haphazard, hut is predetermined in the egg " 

 (p. 225). But here again there is a necessity 

 for evidence, for it still remains to be demon- 

 strated that such asymmetry in the lobster is 

 thus predetermined. The results of some ex- 

 periments made in order to determine whether 

 the crusher could be developed on either side 

 " Zeleny, C, 1905, " Cooipensatory Regulation," 

 Jour, of Exp. Zoology, Vol. II., No. 1. 

 "^ 1907, loc. cit. ( 1 ) . 



of the body by making appropriate mutila- 

 tions during the larval stages, i. e., at a period 

 when the chelas have not yet differentiated 

 into nipper and crusher — may be here intro- 

 duced. Although these experiments are still 

 in progress, some of the data is already signi- 

 ficant because it tends to support a different 

 theory than that of direct inheritance. 



On July 24, 1906, two groups of second- 

 stage larval lobsters were mutilated. In 

 group A, the right chela was amputated, and 

 in group B, the left chela was removed in 

 each specimen. The lobsters were kept in 

 separate compartments and precaution taken 

 to keep a careful record of mutilations, 

 moults, and regenerations for each individ- 

 ual. Such an experiment is especially dif- 

 ficult because the naturally great mortality of 

 larval lobsters when kept in artificial condi- 

 tions is greatly increased by the injury at- 

 tending mutilation, but I succeeded in rear- 

 ing beyond the fourth stage four specimens in 

 group A, and nine specimens in gTOup B. 

 After each moult the regenerated chela was 



GROUP A: EIGHT CHELA REMOVED 



GKOTJP B: left chela REMOVED 



* This specimen was very late in displaying any 

 asymmetrical differentiation, but by November 18 

 the left chela became somewhat broader, showed a 

 characteristic crusher curve in the dactyl and 

 tubercle-like teeth in the proximal region of each 

 jaw. 



f Up to date showed no evidence of having dif- 

 ferentiated into a crusher. 



