140 REPORT OF COMMISSIONERS OF INLAND FISHERIES. 



principles, but we will first observe the points in which there is agree- 

 ment. The pair of extra chelae are mirror images of each other, and 

 the chela nearest the normal claw is also the mirror image of the latter 

 and belongs to the opposite side of the body, i. e., it is a left chela. 



So far the relations seem to conform to the principles of secondary 

 symmetry, but a closer examination reveals a wide variation. The 

 extra pair of chela arise somewhat dorsally of the morphologically 

 anterior surface, and this places in it the position AAD of our diagram. 

 Theoretically, therefore, the extra claws should have their posterior 

 faces opposing each other (the dark sides in the diagramatic sections) ; 

 the claws should be inclined at such an angle to each other that the 

 indices should be brought toward each other and the dactyls thrown 

 apart; and, furthermore, the anterior faces of the normal claw and 

 of the member of the extra pair lying nearest it, should also be in 

 opposition (see diagram). But upon examining the actual specimen, 

 we find these relation to be just the reverse from the theoretical 

 requirements; for instead of the posterior it is the anterior faces of 

 the extra pair which are opposed; in place of the indices, it is the 

 dactyls which are thrown toward each other; and, finally, it is the 

 -posterior, and not the anterior faces of the normal claw and the 

 nearer abnormal chela, which are in opposition. 



At first I was at a loss as to how to account for this apparent 

 contradiction. But finally the idea suggested itself that this whole 

 difficulty could be explained by taking into account the process of 

 "torsion" which takes place during the development of the "great 

 chelae" of the lobster. It is a well-known fact that, both in the 

 ontogeny (Herrick, '05) and in the regeneration (Emmel '06) of 

 the chelipeds, " The terminal segments gradually rotate over and 

 inward," so that a torsion of about 90 degrees is produced and the 

 claw now opens inward on the naturally characteristic horizontal 

 plane" (Emmel, '06, p. 613). This means, therefore, that in our 

 present specimen the upper surface of the normal claw as shown in 

 the drawing should be its morphologically posterior surface, and such 

 is actually the case. But now, curiously enough, it seems that each 



