208 THE BIOLOGY OF STENTOR 



organelles to associate around one frontal field as the grafted 

 animals shifted to produce a normal, homopolar, conical Stentor 

 shape as persisting doublets and triplets. The latter forms may be 

 called biotypes because they regenerated and reproduced as such 



(Fig. 57)- 



One doublet could produce thousands by multipHcation, but 

 after i or 2 months cultivation there was a gradual reversion to the 

 normal single form. Triplets also reproduced themselves and they 

 generally reverted to type in a shorter period, always *' stepping- 

 down " first to doublets and then to singles. Persistence for a long 

 time of these biotypes may be related to their bilateral symmetry 

 and unity of form as expressed, for example, in the presence of 

 but one tail-pole and holdfast.* Faure-Fremiet (1948a) regarded 

 the balance between the two halves of a doublet as imposing a 

 *' structural constraint " on labile transformation back to the single 

 type ; for in such forms as Leucophrys patiila he found that cutting 

 injuries or the diminution of one component led promptly to 

 reorganization as a single individuality. The application of this 

 principle to Stentor is not immediate because the removal of a 

 single set of feeding organelles in doublets merely leads to regenera- 

 tion on the cut side and reorganization on the other, producing 

 the doublet type again. Yet asymmetric doublets are the most 

 likely soon to revert spontaneously to the single type. 



It is doubtless significant that the quadruplet biotype could not 

 be produced. This limitation has also been found in other ciliates 

 (Faure-Fremiet, 1945a). Grafts of 4 stentors could produce tran- 

 sient quadruplets but these did not persist and quickly reduced the 

 oral valency. Unlike triplets, quadruplets could transform at once 

 to giant singles (Fig. 57c) and this was the first indication of the 

 tendency to reduction of oral valency in relation to the number of 

 components grafted, which became increasingly prominent as the 

 size of masses was enlarged. 



The problem of organic individuality is confronted when we 

 ask whether doublets are single or double individualities. They 

 swim and feed and reproduce in a co-ordinated manner like single 

 cells, and there is no further evidence that the two sides of a 



*Uhlig (i960) reported that the one holdfast in doublets is nevertheless 

 doublish or larger than normal, and similarly for triplets. 



