86 Papers from the Marine Biological Laboratory at Torttigas. 



vented from going further by the hard chitinous shell ; this amount of 

 growth (specific amount of regeneration) may very probably be attained 

 some time before the ecdysis. Now, if we follow Zeleny's method of first 

 calculating the specific amount of regeneration and then dividing this by 

 the number of days elapsing between the operation and the molt, we get 

 a slow rate of regeneration for those most injured, since they molt slower 

 and give a larger number of days as a divisor with the specific amount 

 of regeneration as a constant dividend. With such a method of calcu- 

 lation it is not a question of regeneration rate at all, but merely a considera- 

 tion of the molting period. Emmel states that the later the mutilation 

 is made in the molting cycle the more rapid is the rate of ensuing re- 

 generation. This suggests that the regenerating bud may grow to its limit 

 within the encasing wall in a very short time, and when the molt is long 

 postponed it must remain quiescent for a long period. 



I have entered into this somewhat detailed criticism of the work on 

 Crustacea, since it seems to me that in considering the rate of regenera- 

 tion one finds himself on rather uncertain grounds when using an animal 

 on which the continuous growth of the regenerating part can not be ob- 

 served. On the other hand, Cassiopca is well suited to such study, since 

 all of its eight mouth-arms are similar and the regenerating buds from 

 the stumps of the arms grow continuously and may be constantly ob- 

 served and measured. 



Sixteen healthy individuals were selected and their disks carefully 

 measured. They were arranged in eight series of two individuals each, hav- 

 ing one mouth-arm removed from each of the first pair, two arms from the 

 second, and so on to the seventh pair, where seven mouth-arms were removed 

 from each. The eighth pair had four alternate arms removed. After 4 

 days none showed any marked indications of regenerating buds. Two weeks 

 after the operation distinct buds were regenerating from the cut arm-stumps, 

 though at this time it was almost impossible to determine whether there was 

 any difiference in rate. Later, however, diflferences in rate became evident. 



By referring to table 2 comparisons may be readily made between the av- 

 erage specific amounts of regeneration from those medus;e with a few mouth- 

 arms removed and those with many. The first column indicates the num- 

 ber of arms removed from the individual ; the next column gives the 

 diameter of each disk at the time of the operation; the third column gives 

 the specific amounts of regeneration for the medusae 20 days after the 

 operation. This specific amount of regeneration is the quotient obtained 

 when the average length of the regenerating buds from the stumps of the 

 several arms is divided by the aboral diameter of the medusa disk. The 

 fourth, sixth, and eighth columns show the diameters of the medusae 

 at intervals during the experiment. It will be noted that the animals were 



