GROWTH AND DIVISION 89 



ally realized, may be regarded as another manifestation of the 

 persistence of division. I have observed (see Fig. 64A) repeatedly 

 that dividing stentors do eventually undergo fission even though 

 the original process may be cancelled by causing the primordium 

 to be resorbed, or by intervening reorganization or regeneration 

 even with loss of cytoplasm (Tartar, 1958b). The response is as if, 

 once stimulated to divide, a stentor is bound to do so eventually, 

 in spite of intervening catastrophies. This recalls the interesting 

 hypothesis of Swann (1954), originating from studies of egg 

 cleavage. He conceived that, as a separate mechanism, the cell 

 builds up a reservoir of something which is essential to or stimula- 

 tive of division alone, so that this store is depleted only by division. 

 Adapting this idea to Stentor, greatly postponed division could be 

 the consequence of presence and persistence of a reservoir of this 

 factor which is not exhausted by other intervening acts of 

 morphogenesis. 



Reproduction by division in a form like Stentor normally in- 

 volves first the transformation of one individuality into two, 

 followed by the physical separation of the two individualities pro- 

 duced. The integrative tendency of the organism toward unitary 

 wholeness, which theoretical biologists have generally emphasized, 

 is therefore suspended or violated during reproduction in ciliates. 

 From this observation, together with numerous phenomena in the 

 regeneration of multicellular forms, we are led to suppose that the 

 organism is in an important aspect beyond individuality, though 

 tending to individuate as one or more than one, depending on 

 circumstances. Of this we shall have more to say in the con- 

 cluding chapter. For the present it is sufficient to say that 

 "wholeness" is no metaphysical principle which organisms are 

 compelled to maintain and is in fact transgressed every time a 

 stentor divides. 



Stentor also bears on another issue which in the past at least 

 has been prominent in biology : namely, whether a fully differenti- 

 ated cell is capable of division. If not, then regeneration of 

 metazoa would imply either dedifferentiation of cells or the 

 presence of "embryonic cells" still capable of rapid fission and 

 pluripotential differentiation (see Bronsted, 1955). Basing his 

 argument largely upon the fact that apostomatous ciliates undergo 



