EXTENSIONS 365 



divisional Blepharisma was excised, both division and the regenera- 

 tion of the proter proceeded simultaneously, contrasting with 

 Stentor in which regeneration of the anterior daughter is always 

 delayed until after fission is completed. 



These differences are minor, though instructive, and should not 

 be allowed to detract from the demonstration of a remarkable 

 similarity between the two ciliates. In both genera, micrurgical 

 studies show how important is the pattern of the ectoplasm for 

 the course of cytodiiferentiation. 



In the manner of elaboration of cytoplasmic structures Stentor 

 is also not remote from other ciUates (see Klein, 1932; Tartar, 

 1941b; Faure-Fremiet, 1948b; and Lwoff, 1950). Starting with the 

 flagellates from which all agree that the ciliates have evolved, the 

 general picture, as developed by Faure-Fremiet (1954), seems to 

 be as follows. The centrosome was originally developed to produce 

 spindle fibers for mitotic division of the nucleus. In flagellates the 

 centrosome also assumed the new role of producing an external, 

 fibrous flagellum and its associated organelles. By delegating this 

 function to other granules (blephoroplasts) derived from the 

 centrosome and also self-replicating, the number of fiagellae and 

 complexity of organization could be increased. In ciliates, the 

 fibrogenic granules lose their morphological association with the 

 nucleus, increase greatly in number, becoming the semi-autono- 

 mous kinetosomes which produce short fiagellae (i.e., cilia, with 

 the same fibrous structure). The transition form, Opalina, shows 

 uniform ciliation and there is still a certain lack of autonomy in 

 that the basal bodies all stem from one or two generative kinetics. 

 But the large population of kinetosomes and their self-reproduction 

 in ciliates provided the possibility of specialization of the fibers 

 derived from them as well as for the association of parts into 

 organelles. The organelles, specifically the mouthparts (and in the 

 case of Lichnophora^ the pedal disc), in turn become in a manner 

 themselves self-reproducing in that new mouthparts are developed 

 at least in close association with the old. But, just as the kineto- 

 somes become morphologically (yet not physiologically) indepen- 

 dent of the nucleus, so the oral anlagen became more autonomous 

 and, in Stentor, originate far from the preexisting mouthparts. A 

 vestige of the old relationship (as when in Euplotes the new 

 membranellar band always forms near the posterior end of the old) 



