100 REPORT OF COMMISSIONERS OF INLAND FISHERIES. 



IV. Discussion 128 



1. Frequency of Occurrence of these Various Types of Abnor- 



malities 128 



2. Theoretical Significance of these Abnormal Structures 133 



a. Limbs with Paired Extra Process 133 



1. Bateson's Principles of Secondary Symmetry 133 



2. Extra Processes Repeating but One Segment, i. e., 



the Distal Segment or Dactyl 136 



3. Extra Processes Repeating more than One Seg- 



ment 138 



b. Symmetrical Chelae 143 



3. Regarding the Origin of Abnormal Appendages 144 



a. Discussion of the Three Theories that they are: (1) Con- 



genital or Inherited; (2) caused by Injuries sustained 

 after Moulting; or, (3) are Regeneration Products: — 

 with Special Reference to the Regeneration Theory. 144 



b. Further Considerations favoring the Regeneration Theory 147 



1. That the Abnormal Crustacean Limbs found so far 



have been only on Adult Animals 



2. That the Great Majority of these Deformities are 



also found only on the more Distal Segments 



of the Limbs 148 



3. The Regeneration of Extra Legs following an Arti- 



ficial Splitting of Nerves 149 



