REVERSAL OF ASYMMETRY IN ALPHEUS. 2OI 



large chela on the left side. The first moult occurred nine days 

 after removal of the large chela ; Fig. 3, A, shows the cast skin 

 of the original small (right) chela, B, the same appendage re- 

 moved three days after the moult, showing the characteristic fea- 

 tures of the large chela ( transverse groove, shortened and thick- 

 ened chela, and the "hammer"). The second moult occurred 

 six days later ( nine days after the first moult ) ; Fig. 3, C, shows 

 the result, the appendage having returned to its original condition, 

 except in size, while a chela of the large type had appeared on 

 the other side. 



In all cases the hammer-chela on its emergence from the skin 

 of the small chela is less modified than that of a normal animal, 

 always showing characters intermediate between those of the 

 fully developed hammer-chela and the small chela ; and the same 

 is true of the regenerating hammer-chela after both chelae have- 

 been removed. In general the longer the period between the 

 operation and the ensuing moult the greater the modification of 

 the hammer-chela. As may be seen from the figures the re- 

 formed or regenerating hammer-chela is less robust than the 

 fully developed one, the claws are longer and less curved, the 

 transverse groove less pronounced and the setose ridge of the 

 propodus (/. .y.) further removed from the tip of the claw. All 

 these characters become more and more accentuated as the 

 period between operation and moult increases. The shortest 

 observed period in which the regenerating chelae ( after removal 

 of both) showed distinct differences was three days (Fig. I, E}\ but 

 the difference is here still one of size and general development 

 only. After removal of the large chela only the structural differ- 

 ences may become clearly apparent after five days, as shown in Fig. 

 2, G, H (though in this case the remodelled small chela fixed 

 nine days after the moult has probably undergone some further 

 change). In this interesting case the hammer -claw very clearly 

 shows a combination of characteristic characters of the small 

 and large chelae. It still retains on the whole the general pro- 

 portions of the small chela of the male, but is more robust, the 

 claws are somewhat shorter, the transverse groove has appeared, 

 and the " hammer " has begun to form. The most interesting 

 point is the retention of the characteristic setose ridge (ii. ^.) of 



