REPORT OF COMMISSIONERS OF INLAND FISHERIES. 141 



member of the pair of extra claws have in turn also rotated another 

 'dQ degrees during this development; and each of the extra claws has 

 thus come to assume a position practically' at right angles to the 

 normal chela. In a word, we have the remarkable conditions here 

 that, while the normal has rotated in the usual manner through an 

 angle of 90 degrees, each of the extra chelae, or the other hand, has 

 gone through a torsion of 180 degrees. 



Now if we were to turn these three chela backwards again to the 

 position they originally held at the beginning of developmental 

 torsion, it is surprising how closely their relations will then in every 

 respect conform to our principles for secondary symmetiy; for, if 

 in the case of the two extra chela, both claws are rotated 180 degrees 

 on their long axis, the claw nearer the normal chela being turned 

 contra-clockwise and the other claw clock-wise, it will be seen that 

 their anterior faces will then be opposed, and the indices in place of 

 the dactyls will be thrown toward each other. Finally, if in a similar 

 manner we rotate the normal chela clock-wise 90 degrees, it is evident 

 that instead of the posterior, the morphologically anterior faces of 

 the normal and the nearer extra claws will now be in opposition. 

 By thus taking into account the developmental history of the lobster 

 cheliped, it seems clear, therefore, that the morphological relations 

 between the members of this triple chela do not fundamentally con- 

 tradict, but rather furnish a remarkable confirmation of the principles 

 of secondary symmetry as formulated by Bateson. 



This factor of "torsion" does not seem to have been considered in 

 previous discussions of crustacean deformities, but it may possibly 

 serve to clear up other exceptional cases. A case in point is the 

 right cheliped of a lobster described by Faxon (Plate II, Fig. 6) and 

 Bateson (No. 826). With reference to this specimen Faxon states 

 that, "curiously, the supernumerary carpus is set upon the meros 

 in a position almost the reverse of that of the normal carpus .... 

 It is as if the normal carpus were rotated upon the meros nearly 



180 degrees to the left This distortion seems to me very 



singular, and I think nothing like it has been observed among 



