PROCESS OF REGENERATION 



145 



by them runs parallel to the length of time that they were allowed 

 to remain part of the long pieces. 



Experiments of this kind carried out on Planaria dorotocephala 

 (Child, '14 e) yielded the unexpected result that it is determined 

 within six to eight hours after section whether or not a piece of 

 Planaria shall produce a head or remain headless, and within 

 eighteen hours whether the head shall be normal. In the case 

 of Lumbriculus, acephalic pieces are so rare that one cannot dis- 

 cover the time at which head determination occurs; I have 

 therefore merely attempted to find out when the head is deter- 

 mined as normal. As preliminary experiments showed that at 

 least ten hours are required for this, I began my later experiments 

 with a fifteen hour interval. The result of such an experiment 

 are given in table 3. Two hundred long pieces ac were cut from 



TABLE 3 



the posterior ends of worms of the same size and from the same 

 stock; fifty short pieces ab were cut from the anterior ends of 

 these immediately; and fifty more after elapse of fifteen, twenty, 

 and thirty hours respectively. The results are given in percent- 

 ages ; multiple outgrowths are classified under the types of heads. 

 While I regret that I have not a closer series of time intervals, yet 

 I think that it is evident that the head of Lumbriculus is deter- 

 mined as normal in the majority of cases within twenty hours 

 after section, and in practically all cases within thirt.y hours. 



2. Stimulation by section 



As a second step in the analysis of the process of anterior 

 regeneration, one must know what the metabolic condition of the 

 pieces is at the time when the head is determined as normal. 



