658 PROCEEDINGS OF THE AMERICAN ACADEMY. 



(as will be seen from Figure 2), while other arms in the same specimen 

 with the nerve intact have regenerated normally. 3 



There are three possible interpretations of this phenomenon : (1) It 

 may be essential for the regeneration of an arm that the cut nerve 

 should present a free end, as was the case with the earthworm. Or, (2) 

 it may be possible that the undestroyed portion of the radial nerve be- 

 tween the point of injury and the cut end of the arm could furnish 

 sufficient impetus to cause a slight regeneration. Finally, (3) the ex- 

 planation may be that in those cases where the wound was made deep 

 the continuity of all parts of the nervous tissue present in both the 

 superficial and deeper portions of the arm was destroyed. Which ot 

 these explanations is the correct one must be decided by future 

 experiments. 



Experiments by injuring the ring-nerve have not yet been successful, 

 owing to the great difficulty of such an operation. 



Before concluding I wish to mention some of the observations made 

 on the rate of regeneration of arms. This matter was examined from 

 two standpoints : the relation of the rate of regeneration, first, to the 

 level at which the arms were cut, and, secondly, to the number of arms 

 removed. A few specimens represented by Figures 6 to 14 show the 

 nature of the results. If we compare the rate of regeneration of arms 

 cut at the base with that of those cut near the middle of their length, 

 making proper allowance for individual variations, it will be almost im- 

 possible to say which regenerates most. On the other hand, comparing 

 arms cut off at the base, or at the middle (Figures 7, 11, 13, and 14), 

 with those cut off near the tip (Figures 6 and 10), the difference in the 

 rates of regeneration becomes very striking. The total amount regener- 

 ated during the same period is much greater in the case of the shorter 

 stubs than in the case of the very long one ; indeed, it would not be an 

 exaggeration to say that the greatest regeneration from the arm cut 

 near its tip does not exceed the least regeneration from one cut at its 

 middle. These results are in perfect agreement with Miss King's 

 results on the regeneration of arms in Asterias. 



As regards the second point — the relation of the rate of regeneration 

 to the number of removed arms — my experiments with brittle-stars 

 from which 1,2, 3, 4, or even 5, arms had been removed by being cut 

 off at the base, do not fully conform to Zeleny's rule, which was based 



T 



3 Miss H. D. King, working on the regeneration of the star-fish, found that 

 on cutting the arms horizontally just above the vertebral ridge the edges of 

 the dorsal parts curled under, but did not regenerate, while the ventral parts, 

 containing the radial nerve, reproduced a new dorsal surface. 



