8O A. B. DAWSON. 



resemblance to the abnormal chelipeds figured by Emmel 

 ('07, PI. 2, Fig. 5) and Cole ('10, Figs, i, 2) also presents several 

 novel features. The degree of "triplication" of the claw is less 

 than that seen in Emmel's specimen but greater than that de- 

 scribed by Cole. In the former, the abnormal processes, con- 

 sisting of a double carpopodite, two protopodites and two dactyls 

 arose from the meropodite. In the latter, the abnormal struc- 

 ture, two extra indices and a double extra dactyl, was borne on 

 the normal protopodite. In Faxon's specimen ('81) the mor- 

 phological character of the extra branch which is borne on the 

 forked meropodite is questionable. Faxon himself does not 

 believe that the structure is double but Bateson ( '94) is inclined 

 to regard it as being morphologically double. Furthermore 

 both Emmel and Cole found that the conditions in their "triple" 

 claws illustrate the rules of secondary symmetry almost diagram- 

 matically, i.e., when allowance was made for shifting due to 

 torsion. 



In the two chelae described by Emmel and Cole the two extra 

 claws were of the same character as the primary claw, "crushers." 

 In my specimen the primary claw is a "nipper" while the two 

 extra claws are of the crushing type with well-developed tubercle- 

 like teeth. This condition is of special significance, when we 

 recall that the claw of the opposite side is also of the nipping 

 type. In other words, we have a lobster with the "great" claws 

 symmetrical with reference to each other, besides bearing on the 

 meropodite of the right a double extra "crusher." 



Emmel ('07) finds the pigmentation reversed on one of the 

 extra claws but is able to explain this abnormal condition by a 

 reference to torsion. The case which I am describing does not 

 admit of such an explanation. The cause of the abnormality 

 is unknown. No scars were to be found on the "triple" claw, 

 but on the protopodite of the appendage of the opposite side a 

 definite scar (S) was present. There were no further evidences 

 of mutilation. 



The results obtained by Harrison ('17) with transplantation 

 of limb buds in Amblystoma larvae suggest that there may possibly 

 be some direct relation between the reversal of pigmentation and 

 the doubling of the extra appendage. Harrison found that in 



