ACTIVATION AND INHIBITION: ORAL PRIMORDIUM 147 



A 



Fig. 37. Oral inhibition of primordium development. 



A. Stage-2 regenerator is recapped with head from another 

 stentor. By handling only pendent portion of donor, which is 

 subsequently excised (a), injury to feeding organelles is 

 prevented, b: Development is stopped and the anlage resorbed. 

 This occurs neither on injury, alone, of regenerator nor after 

 implanting tail poles; therefore a specific inhibition by formed 

 oral structures. Most specimens reorganized later {c, d), and 

 some divided instead. 



B. When primordium was already at stage 4, it was not 

 resorbed (a) and served for reorganizational replacement of the 



grafted feeding organelles. (After Tartar, 1958c.) 



Reorganization and division would then be like regeneration in 

 that the oral structures may be "self-excised", and if so, the 

 regeneration response to cutting off the head or mouthparts would 

 be not so much an adaptive behavior as a gross imitation or 

 artificially induced performance of something that happens 

 cryptically in the recurring processes of fission and reorganization. 

 This in turn would at last answer Gruber's (1885a) question why 

 stentors should be so capable of regenerating from injuries such as 

 they are not likely to encounter in nature, as well as explain to a 

 considerable extent his original conception of the close similarity 

 between regeneration and division, a point repeatedly emphasized 

 by later students of ciliate morphogenesis (see Balamuth, 1940). 

 We need to learn how these formed feeding organelles exert the 



