HETEROCHELY 189 



heterogony of a character and its restriction to one sex. It 

 will be clear, however, from our previous discussion that 

 heterogony is a quite general phenomenon, and that it is 

 merely very obvious in many secondary sexual characters be- 

 cause these are frequently of an exaggerated nature, demanding 

 high growth-ratios for their development. 



§ 5. Heterochely and Relative Growth-rates 



Some suggestive facts concerning differential growth emerge 

 from the experiments on heterochelous Crustacea, which have 

 been summarized and interestingly discussed by Przibram 

 (1930). As is well known, in forms like Alphaeus, while ampu- 

 tation of the small or nipper claw is followed simply by the 

 regeneration of a new nipper, with no change in the crusher, 

 amputation of the crusher is followed by a reversal of the 

 type of claw, the old nipper growing into the new crusher, 

 the claw which regenerates in place of the old crusher growing 

 into the new nipper. (This, it may be recalled, is closely 

 parallel with the results of Zeleny (1905) on the polychaete 

 Hydroides. This sedentary worm has paired opercula, of 

 which one is large and functional, the other rudimentary. 

 Amputation of the large operculum causes the rudiment to 

 grow into a functional organ, while the amputated organ 

 regenerates of rudimentary type.) In certain other hetero- 

 chelous Crustacea, such as the lobster (Homarus), it was long 

 supposed that amputation of the crusher was not followed by 

 this reversal. But later work has now shown that this only 

 applies to later stages : if the operation is performed on quite 

 young animals, reversal does occur. And it now seems to be 

 a general rule that reversal will occur at small sizes in all 

 heterochelous forms, although the size-range over which it 

 occurs differs considerably from form to form. In some cases 

 no reversal is possible after quite a young stage. In others, 

 like Alpheus, it can occur throughout life. In both Homarus, 

 in which the crusher (like the large chela of male Uca) may 

 be either on the right- or left-hand side at random, and in 

 the crabs Portunus and Eriphia, in which the crusher is nor- 

 mally always on the right, reversal can only take place before 

 visible differentiation of claws has occurred. The result of 

 amputation of future crusher in such cases is that the other 

 claw (as in young Uca, where, however, both chelae are similar, 

 of male type) becomes the crusher, while the amputated 

 claw regenerates as a nipper. 



