364 THE BIOLOGY OF STENTOR 



of the cell induces invagination and mouthparts formation in a 

 terminus of the primordium which lies in or near it. 



Homopolar primordium sites are obviously capable of forming 

 anlagen though not in their normal position. Heteropolar pieces 

 tend to creep apart, showing that their polarities are intrinsic and 

 retained. As in stentors, heteropolar primordium sites may not be 

 activated to produce anlagen and smaller reversed patches may be 

 resorbed. When longitudinal halves are rotated upon each other, 

 an extra primordium may appear at the suture, and this indicates a 

 possible inductive action between these stripe areas as at loci of 

 stripe contrast in stentors. 



The chief differences in morphogenesis in Stentor and 

 Blepharisma are now noted. In the latter, Suzuki speaks of an 

 evident ** growth zone" at the posterior end of the developing 

 anterior daughter cell which forms a new posterior end during 

 fission. Such is not obvious in stentors, in which Johnson only 

 indicated that something like this increase may occur. Possibly 

 related to the occurrence of this zone is Suzuki's finding that the 

 oral parts in Blepharisma induce V-areas or primordium sites in 

 any indifferent region lying posterior to them. Thus, when the cell 

 was transected and feeding organelles shifted to the side opposite 

 the original primordium site, a new site then developed posterior 

 to the displaced organelles and doublets were produced. This does 

 not occur in Stentor \ for if the head is rotated 180° the anlage 

 appears only in the original primordium site and a new site is not 

 generated posterior to a displaced mouth. Also, in Stentor doublets 

 converting to singles, a primordium site may be obliterated 

 posterior to one of the mouths, which remains intact. 



Doublet animals behave differently in other ways. Removal of 

 one set of mouthparts did not result in regeneration in Blepharisma. 

 Apparently one set of organelles can inhibit anlagen formation in 

 two primordium sites; but in stentors double regeneration- 

 reorganization always occurred if one site was not subtended by a 

 set of mouthparts. Blepharisma doublets could not remodel 

 directly into singles, as stentors do. They achieved this end rather 

 by exaggerating their doubleness and splitting apart from the 

 anterior end. Hence these two ciliates exemplify the two types of 

 transformation to singles defined by Faure-Fremiet (1948b). 

 Finally, it may be noted that when the anterior end of a pre- 



