138 THE BIOLOGY OF STENTOR 



or remain incomplete. Examples of this abortive development will 

 be noted later. 



A state of inhibition can therefore adversely affect primordium 

 development at any stage until final oral structures are formed, 

 or conversely, a state of activation is essential during all this time. 

 The initial appearance and preparation of the anlage also requires 

 activation. For incipient regenerators at what may be called 

 stage O will not even begin primordium development if grafted 

 to inhibitive, non-differentiating partners. The inhibition is in 

 fact then so strong that the regenerator usually does not begin 

 regenerating until the following day. 



Returning again to our typical experiment, consider now what 

 happens to the regenerating stentor after the primordium sector 

 has been removed. A new anlage can appear within one hour, 

 although an hour and a half is closer to the average interval. 

 This precipitous re-formation of the anlage is most simply ex- 

 plained on the basis that the cell was already activated. 



An accelerated renewal of the anlage of a quite different order 

 of magnitude (6 vs. 9 hours) was noticed by Weisz (1956) in 

 comparing dividers, which had resorbed their primordia because 

 of injuries, with injured pre-fissional animals. This time difference 

 he attributed to the persistence of an " anarchic field " or multiplied 

 store of new kinetosomes which remain ready to supply materials 

 for the new primordium. Yet, when an anlage is resorbed there 

 is no rift left in the ectoplasm to indicate that kinetosomes remain, 

 and one would expect an "embryonic" anarchic field also to be 

 resorbed since the earlier and more nascent the primordium the 

 more easily it is resorbed. Moreover, in regenerators in which a 

 new primordium could appear within the surprisingly short time 

 of a single hour, a relatively large sector bearing the anlage was 

 excised so that any anarchic field adjacent to the primordium 

 would also surely have been removed. For in the related Fahrea 

 the new kinetosomes lie between the kineties immediately adjacent 

 to the anlage and in Stentor they seem to be coincident with the 

 primordium itself (Villeneuve-Brachon, 1940), so it should be 

 impossible to cut out the anlage without also removing its progen- 

 itors. I therefore cannot agree with Weisz's explanation, nor accept 

 his claim to have effected this separation of primordium and 

 precursors in other experiments. The long preparatory period of 



