Il8 THE BIOLOGY OF STENTOR 



at the rate of about one stage per hour and the total time for 

 regeneration from the moment of cutting is around 8 to lo hours 

 (Weisz, 1955). What may occur during the preparatory period is 

 discussed later (p. 138). 



In a study of several ciliates other than Stentor but including 

 the spirotrichous Spirostumumy Sokoloff (19 13) stated that the 

 larger the fragment the sooner it regenerates, but his data indicate 

 that differences appear only when there is a marked disparity in 

 size of the pieces. The differences were explained on the basis 

 that a hypothetical physiological harmony has to be established 

 before regeneration and that this, rather than regeneration itself, 

 takes more time to accomplish in tiny fragments. Weisz (1948a) 

 did not find such differences in Stentor coeruleus and stated categor- 

 ically that, other conditions being the same, the time for both oral 

 and holdfast regeneration is independent of the initial size, pro- 

 vided the piece is large enough to permit any regeneration. In a 

 recent series of tests I have found, however, that when the head 

 and tail-pole of coeruleus were excised and regeneration times 

 measured for the main cell body and its own polar fragment the 

 time for the initial appearance of the oral anlage was with two 

 exceptions always greater in the smaller pieces, and the difference 

 was often considerable (unpublished). Size therefore may have a 

 bearing on regeneration rates. 



The same tests — in which the posterior fragment was 

 " favored " by the holdfast — render questionable Weisz's (1948a) 

 contention that the presence of a foot increases the speed of oral 

 regeneration. Therefore, Child's (1949) criticism of this point also 

 may be valid. 



In aboral, longitudinal halves which lack the normal primordium 

 site Weisz (1951b) found that oral, pedal, and contractile vacuole 

 regeneration were much delayed — oral, as much as 30 to 40 

 hours. He attributed this delay to the time required for other 

 stripes to assume the morphogenetic role normally played by those 

 in the part removed. I too have found that the preparatory period 

 in such fragments is usually very protracted, but there appear to 

 be contradictions that need resolving because this was not always 

 the case and some of these fragments did regenerate promptly 

 (Tartar, 1956c). Likewise, when only the primordium site was 

 removed along with the mouthparts, the time for beginning 



