CHAPTER VIII 



ACTIVATION AND INHIBITION OF 

 THE ORAL PRIMORDIUM 



When a stentor which is in the process of developing an oral 

 primordium is intimately grafted to a normally feeding partner 

 not producing a new set of feeding organelles, both animals no 

 longer continue on their original ways but now act upon each 

 other with significant and visible consequences. These inter- 

 actions were first explored in fusions of regenerating to non- 

 diiferentiating stentors. Regenerators often caused the partner to 

 produce a primordium and undergo parallel reorganization. This 

 type of interaction may be called induced reorganization as 

 formulated by Weisz (1956). Alternatively, the influence may 

 proceed in the other direction, suspending the regeneration and 

 causing the regenerator to resorb its anlage. This reaction may be 

 referred to as induced resorption of the primordium (Tartar, 

 1958b). Another way of exhibiting these interactions is to graft 

 cell sectors bearing primordia on to various hosts. When grafted 

 to stentors which are themselves undergoing regeneration, the 

 extra primordia are accepted, supported, and continue developing; 

 but if implanted on to non-diflFerentiating stentors primordia are 

 resorbed though the patch itself is incorporated into the lateral 

 striping of the host. 



The range and basis of these reciprocal influences have been 

 quite extensively explored (Tartar, 1958b, 1958c). The results can 

 be explained in terms of two contrasting cell states: activation, in 

 which something of the whole cytoplasm is involved in supporting 

 primordium formation and development, and inhibition, which is 

 equally pervasive and tends to block or counteract the processes of 

 cell redifferentiation. Either of these states is sufficiently potent 

 to spread from one cell to another with which it is intimately 

 joined, in the one case to force a precipitous primordium formation, 

 and in the other, to cause the complete resorption of an anlage 

 which is already well begun. 



K 



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