Studies of Tissue Growth 447 



stops until the molt occurs. Zeleny takes this constant specific 

 amount of regeneration and divides it by the number of days 

 elapsing between the time of operation and the molt and considers 

 the quotient to be the specific rate of regeneration per day. As 

 mentioned above those specimens most injured molt soonest and 

 therefore give a smaller number of days as a divisor to go into the 

 constant dividend and so their specific rate of regeneration seems 

 faster than that of those individuals less injured v^hich molt slower. 

 This method of calculation is incorrect unless it be proven that the 

 regenerating buds grow continuously during all the days preced- 

 ing the molt. In Zeleny's experiments the number of days be- 

 tween the operation and the first molt varies from 27 to 181 and 

 yet the specific amounts of regeneration were always the same at 

 the time of this molt. It would seem much more probable that 

 this amount of tissue was formed soon after the operation and then 

 stopped by the limiting body wall, than that one arm had required 

 almost seven times as long to regenerate a given amount as another. 



Emmel's ('06) work on the lobster shows that Zeleny neglected 

 an important factor in failing to note the time elapsing between 

 the previous molt and the operation. Emmel found that "the 

 later the time at which regeneration begins after the molt, the 

 greater the length of the entire molting period." Another fact 

 of prime importance shown by Emmel's results was that the regen- 

 eration process itself, and not the mutilation, caused the lengthen- 

 ing of the period between molts. "The average length of the 

 molting period for those lobsters in which the mutilations were not 

 succeeded by the regeneration of the limbs, was not only less than 

 the length of the molting period for the regenerating specimens, 

 but also in a large proportion of cases was even shorter than the 

 molting period for the normal lobster." By "molting period" 

 Emmel means the time elapsing between molts, the expression 

 generally means the time at which ecdysis occurs. 



The question as to the relation between the rate of molting and 

 the rate of regeneration put by Zeleny ('05, p. 362) is answered by 

 the above paragraph quoted from Emmel. The process of molt- 

 ing is affected directly by the process of regeneration itself and not 

 bv the mutilation. 



