142 REPORT OF COMMISSIONERS OF INLAND FISHERIES. 



insects" (p. 263). Bateson placed this specimen under his list of 

 "exceptional cases" and offers no explanation for the unusual condi- 

 tions pointed out by Faxon. It seems clear, however, that the rela- 

 tions which Faxon regarded as very singular in this case may be 

 adequately accounted for as the result of the torsion of the normal 

 and abnormal chelae during their development.* 



Specimen No. 7. (See diagram, Fig. IV, position VVP.) 



In this specimen the extra parts appear to arise slightly posterior 

 to the ventral surface of the leg. It will be seen in the diagram for 

 this position that the two extra claws should be inclined to each 

 other at an obtuse angle of at least 150 degrees. But in specimen 

 No. 7 there is a great variation from this; for instead of 150 degrees, 

 the two extra claws are inclined to each other at an angle of not more 

 than 45 degrees, — a relation which corresponds to a more posterior 

 point of origin (see diagram, Fig. V, position PPV). Furthermore, 

 the relation between the minor images also correspond to a point of 

 surface origin farther posterior than is apparently actually the case. 

 While this specimen, therefore, seems to furnish a variation from the 

 above principles, is should, however, be taken into consideration that 

 a severe injury was sustained by these extra claws during their re- 

 generation and that, consequently, this variation in relations may 

 be largely due to an interrupted development in which the two claws 

 were inhibited from diverging in their angular relations as widely as 

 they might otherwise have done. 



On the whole, then, we may conclude the discussion of these six 

 cases of abnormal appendages with the observation that with a few 

 minor exceptions these six specimens conform to a remarkable degree 

 with what might have been theoretically predicted, and that they 



♦Since writing the above paragraph I have re-examined Bateson's work and find that he has 

 suggested explaining certain irregularities among vertebrate Hmbs in something of a similar 

 manner. He observes that in the case of double hmbs among vertebrates, "there is generally 

 a relation of images between the extra pair," but " a definite geometrical relation between them 

 and the normal limb is seen more rarely." And he suggests "that this may be in part at least 

 attributed to the normal twisting of the vertebrate hmb, especially of the hind limb, from its 

 original position" (p. 556). 



