ACTIVATION AND INHIBITION: ORAL PRIMORDIUM 151 



These are only a sample of many observations (unpublished) in 

 which synchronous development within the same system by arrest 

 of one primordium, or acceleration of the other, or both occurred. 

 But if the phase difference between the two anlagen is great, 

 simultaneity cannot be achieved and the older primordium 

 overtakes the much younger one, causing the system to pass into 

 a state of morphogenetic inhibition, resulting in resorption or 

 very incomplete development of the younger anlage (Fig. 38E). 



Synchronization of primordia, often involving astonishing 

 accelerations and delays in development, should have important 

 implications which are only coming into view. For one thing, it is 

 clear that each primordium is not given a start and a source of 

 substrates and a suitable environment to proceed on its own. 

 Instead, the two primordia are as it were in continuous "com- 

 munication" with each other though they may be at opposite 

 sides of the cell. One suggestion that comes to mind is that there 

 is a competition for substrates which the younger primordia are 

 able to take up more avidly. But the supply does not seem to be 

 limited, since induced primordia are formed and present anlage 



B. a: Telebiotic with narrow connection has stage-3 anlage 

 at end from which the feeding organelles were excised, b: 

 Original primordium at stage 5 ; induced anlage appeared at other 

 end and developed precipitously to stage 4. c: Both anlagen 

 synchronized at stage 6 and regeneration with induced 



reorganization continues. 



C. a: Smaller non-differentiating stentor grafted to stage-3 

 regenerator, b: Original anlage now in stage 4 and induced 

 reorganization primordium has developed so rapidly that it is 

 now in the same stage, c, d: Synchronous regeneration and 



reorganization to produce a doublet. 



D. a: Stage-3 divider, with mouthparts excised, grafted to 

 non-differentiating stentor of same size, b: Division primor- 

 dium develops to stage 4 but becomes crumpled as it is arrested 

 and waits for induced reorganization to attain the same stage. 

 c: Synchronous regeneration-reorganization proceeds from 



stage 4 onward. The graft complex did not divide. 



E. Stage-5 regenerator grafted to non-differentiating partner. 

 A reorganization primordium is induced {a) in the partner, but 

 the regenerator continues development and passes out of the 

 stage of activation. Thereby induced anlage is "overtaken" and 

 can neither develop to normal length nor produce mouthparts 



to replace those resorbed. 



