REVERSAL OF ASYMMETRY IX ALPHEUS. 2O/ 



structure of the small chela, which differs widely in the two 



sexes. 1 



In the female A/phcns this appendage is distinctly less modi- 

 fied than in the male (Fig. 2, D], being of slender form, with the 

 claws straighter, weaker and longer. In the male (Fig. 2, A), 

 the chela is of more robust form, the dactylus is more curved, 

 and bears on each side a prominent curved ridge armed with a 

 close series of strong setae, while the fixed claw of the propodite 

 has on each side a similar but straighter and weaker ridge also 

 covered with setae. Both these ridges are absent in the female. 

 A comparison of Figs, i, A, B, 2, A, D, clearly shows that in 

 some of these respects the small chela of the male is intermed- 

 iate in type between that of the female and the large chela, 

 which is essentially of the same type in both sexes. This ap- 

 pears in the robuster form of the male chela, the occasional pres- 

 ence of a slight transverse groove on the propodus corresponding 

 to the deep groove on the large chela, the greater thickness and 

 curvature of the dactylus, and the much greater prominence of the 

 seta-bearing ridge on the claw of the propodus, which obviously 

 corresponds to the prominent setose ridge in the corresponding 

 position on the large chela. The female small chela is obvious!), 

 of more generalized type ; and as far as can be judged from the 

 figures of Brooks and Herrick is closely similar to both chelae of 

 the larval form, on their first appearance. 



With these points in mind it is interesting to compare the 

 chelae of an animal after the first moult subsequent to removal of 

 the large chela. In botli sexes the small chela, regenerated from 

 the stump of the large one, is of the female type (cf. Figs. 2, D, 

 C, /*) while in both the re-forming large chela is intermediate in 

 form between the fully developed large chela and the small chela 

 of the male. Furthermore, a comparison of the large chela, in 

 regenerated individuals, shows in general that the longer the 

 period after the operation, the greater its divergence from the 

 small chela. Consideration of the sexual differences brings out 

 the further interesting fact that the transformed small chela of the 

 male for the same period of time is more highly modified than 

 that of the female. This is clearly shown by a comparison of 



1 Cf. Coutiere, " Les Alpheidze," Ann. Sa. Nat. Zoo!., VIII., 9, 1899. 



