NATURAL, HISTORY OF AMERICAN LOBSTER. 
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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 asymmetry 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 1901-2 Przibram (221) showed 
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 (9a) 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 
