TOWARD A GENETICS OF STENTOR 



321 



appeared altogether normal, and it seemed to be of the usual length, 

 including the part which descends into the gullet, because this 

 band curved into a long spiral (Fig. 92). If this appearance is 

 correctly interpreted, then normal length of the row of membra- 

 nelles is not used as a sign that successful oral differentiation has 

 been completed; for regeneration or reorganization then followed. 



Fig. 92. Astomatous primordium development in Woods Hole 

 race of S. coeruleus. Normal animal reorganizes, producing 

 peristomal anlage of normal length which fails to invaginate to 

 form mouthparts. Following regeneration now produces 

 complete mouthparts. Animal feeds and divides, forming 

 daughters with complete feeding organelles but each having one 

 unusually large macronuclear node. 



with the production in the same individual, usually on the first try, 

 of good mouthparts. The animals could then feed, explaining why 

 the abnormality did not result in its own extinction but persisted 

 in the subcultures for about a year, after which only normal 

 animals have been found. Astomatous stentors appeared normal 

 in other respects except for a variability in size of the macro- 

 nuclear nodes, and analysis of this trait is the more difficult because 

 the same individual could manifest both the complete and incom- 

 plete development of the feeding organelles. Isolated normals 

 could pass through the mouthless phase while astomatous indivi- 

 duals later became normal. Anterior and posterior fragments did 

 not differ significantly in the frequency with which they regenerated 

 incompletely. Until this abnormality reappears and can be studied 



