APPENDIX. 



After the present paper had gone to press Dr. Zeleny published the re- 

 sults of a study on the effect of degree of injury, successive injury, and 

 functional activity upon regeneration in the scyphomedusan Cassiopea 

 xamachana} In this paper he concludes that " removal of six of the eight 

 oral arms constitutes the most favorable degree of injury for the regenera- 

 tion of each arm, and that from this optimum there is a decrease in both 

 directions." The data, however, on which this statement depends is not 

 altogether conclusive. One finds on studying his table that the extremes of 

 variation in regenerative rates among similarly injured individuals are in 

 the large majority of cases greater than the differences between the average 

 specific amounts of regeneration for two groups of individuals injured to 

 different degrees. With such a wide range of variability shown among 

 the few individuals one is uncertain as to the real significance of the table. 

 Nevertheless, the data do seem to show a steatly advance in specific rates 

 of regeneration up to a maximum where six arms were removed. 



In a general way my results on regeneration of the oral arms might also 

 be interpreted, like Zeleny's averages, to show a gradual increase in regen- 

 erative rates with an increase in degree of injury. Zeleny seems inclined 

 to emphasize the importance of this apparent increase in regenerative rates, 

 while I believe the great range of variability in the regenerative rates shown 

 by the small number of individuals studied should not be overlooked and 

 that it renders a general conclusion from such observations very uncertain. 



Zeleny's study of the effect of the rhythmical pulsation of the medusa 

 disk on the rate of regeneration may be compared with my experiments 

 bearing upon the same subject. Our results agree and both indicate, con- 

 trary to the view of some observers, that functional activity is negative in 

 its influence on the rate of regeneration. Zeleny compared the regenerat- 

 ing margins and centers of medusce disks pulsating rhythmically with those 

 from other medusae at rest, and found that in four of the six pairs of cases 

 the non-pulsating individuals regenerated faster than the pulsating ones. 

 In the fifth pair the two were equal, and in the sixth the pulsating individual 

 regenerated faster. 



The question might arise whether in my own experiments the influence 

 from the pulsating half may not be conveyed to the resting half. Improb- 

 able as is such a view in itself, the interpretation is negatived by my con- 



' Journal of Experimental Zoology, v, 2, pp. 265-274. 1907. 



