REGENERATION II7 



with two complete sets of feeding organelles I found that if one of 

 the mouthparts developed incompletely, or if one mouth was 

 excised, or if one complete set of feeding organelles was removed 

 without leaving remnants behind, then the remaining set, normal 

 and fully formed, still did not prove sufficient. Regeneration always 

 occurred on the defective side with simultaneous reorganization 

 on the other. The only time when this did not take place was when 

 the doublet was transforming into a single stentor and one of the 

 primordium sites was disappearing (Tartar, 1954). Regeneration 

 therefore may be said to occur whenever a primordium site is not 

 subtended by a complete set of feeding organelles normally joined 

 together in one unit. 



4. Time for regeneration 



Clocking the time for regeneration may afford some hint 

 regarding the nature or the order of magnitude of the processes 

 involved. At least we can designate the minimum period within 

 which any postulated reaction must be able to accompUsh a visible 

 result, and this should offer some guide to hypothesis. A point 

 which is obvious, yet perhaps deserving explicit statement, is that 

 regeneration of lost parts is enormously more rapid in ciliates than 

 in multicellular animals. 



We have noted that an excised tail-pole and holdfast in Stentor 

 coenileus can be re-formed in one to two hours, and little or no 

 synthesis of new structures may be involved. Relating oral as well 

 as pedal regeneration to temperature, Weisz found that lowering 

 the temperature 10 degrees increased the time by a factor of about 

 1-6. He also claimed that the presence of intact feeding organelles 

 hastens foot formation, yet it is possible that such formations are 

 retarded when the head is excised merely because an added burden 

 is thrown upon the cell (Child, 1949). 



Oral regeneration is by elaboration of a primordium and requires 

 more time. An important distinction was emphasized by Weisz 

 when he separated a preparatory period, as the interval between 

 excision of parts and the beginning of anlage formation, from the 

 time required for the development of the primordium itself. The 

 former he found to require about 4 hours as a rule, though the 

 figure can be pushed closer to three if one is careful to watch for 

 the inconspicuous stage- 1 anlage. Development then proceeds 



