ACTIVATION AND INHIBITION: ORAL PRIMORDIUM 149 



important point is that the development of the oral primordium 

 is not a strictly local affair except in morphological terms, that the 

 entire ectoplasm appears to be a continuum, that every part of this 

 ectoplasm — even far from the primordium site — can affect the 

 primordium development by either hindering or supporting it, 

 depending on the intrinsic state of that cytoplasm. 



5. Synchronization of developing primordia 



In stentor grafts or complexes of more than one individuality 

 there is a strong tendency for both or all oral primordia to com- 

 plete their development together although they may have begun 

 at different times. This synchronization was first indicated by 

 Johnson in his observation of redifferentiation in an adventitious 

 double-tandem monster of coeruleiis. The anterior individuality 

 had a complete set of feeding organelles but the posterior lacked 

 the mouthparts. An anlage first appeared in the posterior compo- 

 nent, then somewhat later primordium formation also occurred 

 in the anterior component which had no need for regeneration; 

 but in spite of the difference in the time of their appearances the 

 two primordia soon fell into phase and developed simultaneously. 

 This case may therefore be regarded as the first observation of a 

 regenerator inducing reorganization in its partner ; and it suggested 

 that in such double systems both parts tend to do the same things 

 together and at the same time. 



Even within a single primordium the parts tend to develop 

 together when they might do otherwise. Thus if half of an early 

 anlage is excised there is a compensating growth in length of the 

 primordium but a difference between younger and older developing 

 membranelles is not detectable (Tartar, 1957c). Evidently the 

 older part waits while the growth of the new part is accelerated. 

 This effect is still more striking in cases in which an original 

 primordium later extends into a new primordmm site which is 

 often produced by graftings. This and other examples described 

 in Fig. 38 show how an anlage extension or an induced re- 

 organization primordium may differentiate very rapidly in order 

 to catch up with the first anlage, often apparently cutting short its 

 growth in length in its haste to develop. Converselv, in the achieve- 

 ment of simultaneity of development, arrest and delay of one of 

 the anlagen is often noticeable. 



