NATURAL HISTORY OF AMERICAN LOBSTER. 277 



can both produce and restore a condition of symmetry. Both Przibram (221) and 

 Morgan (203), as well as Emmel, have called attention to the fact that when the crushing 

 claw is thrown off the regenerated member at first suggests a transitional stage between 

 the more primitive toothed and the more modern crushing type, but this is not always 

 the case, for two of Emmel's lobsters developed similar crushing claws at a single molt. 

 Emmel's experiments show that a change in the type of big claw may occur in the adult 

 lobster, but whether this is to be regarded as a step in the process of complete reversal 

 of asjnnmetry met with in the younger stages of Alpheus and other forms described by 

 Przibram remains to be seen. As Wilson has already remarked, the removal of both 

 forceps from the prawn, unlike the case of the lobsters referred to, led to no disturbance 

 in the normal asymmetry of those appendages. In 1 901-2 Przibram (221) show'ed 

 that in the crabs similar claws could be experimentally produced through regeneration. 



To follow the reversal phenomena of Alpheus more closely for comparisons: We 

 have seen that this shrimp carries a huge "hammer" or snapping claw, which in some 

 species is as large as the entire body of the animal, and a diminutive claw of more primi- 

 tive form on the opposite side. Moreover, in the common Alpheus heterochelis of the 

 southern coast the small chela presents an interesting sexual variation, and resembles 

 the "hammer" more closely than does the corresponding simpler and more primitive 

 claw of the female. 



A striking example of heteromorphic regeneration or reversal of asymmetry is seen 

 when the Alpheus "shoots" its "hammer," or for any cause loses its big claw, as was 

 discovered by Przibram in 1891. The big claw seems to hold the little one in check, 

 for no sooner is it lost than the smaller one grows apace and becomes differentiated into 

 a "hammer " or "snapper," while, as if in compensation for this change, a diminutive chela 

 of the primitive type replaces the great claw lost from the opposite side. Wilson {284) 

 found that in both sexes the small claw, which was regenerated from the stump of the 

 large one, was always of the simpler female type, and, moreover, that the small chela of 

 the male was more rapidly changed into the big ' ' pistol ' ' or hammer claw because it was 

 already further advanced on this line of development than that of the female. When 

 the smaller claw is amputated, or when the "forceps" are removed from both sides of 

 the body at once, there is no reversal, a new slender chela or hammer claw taking the 

 place of the corresponding member lost. Many additional facts have been brought to 

 light through the experimental studies of Wilson, Brues, and Zeleny. 



Przibram {223) has also found by experiment that reversal of the claws takes place 

 not only in Alpheus, but also in Athanas, Carcinus, Callianassa, Portunus, and Trypton; 

 that the tendency is most marked in the younger stages, and that it decreases with age. 

 His results are therefore similar to those obtained by Emmel (92) in the lobster, where 

 the experimental control of asymmetry ceases, as we have seen, at the fourth stage. 



In the lobster no reversal or compensatory regulation normally or usually attends 

 the regeneration of any of its appendages. The crushing or the toothed forceps, when 

 severed at the "breaking plane," are as a rule replaced by their like in due time after 

 one or more molts. How, then, are we to explain the anomaly of similar claws? It 



