376 THE BIOLOGY OF STENTOR 



bound to the cytoplasm by any intimate structure and requires no 

 specific geometric relationship with the cytoplasm for its eflfective 

 action, Prowazek (1904) inferred that there is only a substance 

 relation between the two phases of the cell which could well be 

 explained in chemical terms. Neither can the form of the cell, nor 

 that of the organism in the case of protozoa, be related to the 

 flowing endoplasm which indeed has been shown in Condylostoma 

 (Tartar, 1941b) and in the regeneration of stentor "skins'* 

 (unpublished) to be dispensable. Therefore nucleus and cytoplasm 

 presumably interact by chemical contributions to each other, and 

 guidance of the elaboration of formed parts in the cytoplasm is to 

 be sought in neither a nucleus of unprescribed location nor a flowing 

 endoplasm but in the most solid portion of cell, namely, the 

 ectoplasm (Prowazek, 19 13). 



Events in the ectoplasm of Stentor also clearly exert control 

 over the behavior of the nuclei. Micronuclei divide whenever an 

 oral primordium is formed, even when there is no cytosomal 

 fission. Macronuclei coalesce, re-nodulate, or are divided according 

 to the phase of the cytoplasm in which they find themselves. 

 Compensatory increase in macronuclear volume occurs only if 

 primordia are formed. And the disposition of the macronuclear 

 nodes is evidently determined in large part by the pattern of 

 ectoplasmic striping. 



The cytoplasm may have its own replicating units, including 

 kinetosomes as important elements of ectoplasmic structure. Self- 

 reproducing entities are of limited explanatory value because they 

 refer us back to another of the same type of entity which we seek 

 to analyze and explain. Yet to establish a genetic continuity of 

 cytoplasmic parts would tell us whence new entities arise, i.e., 

 from preexisting ones, and this is a great aid in narrowing the field 

 of inquiry. Moreover, replicating units and their elaborations alone 

 would not make an organism but merely an assemblage. '' Is 

 anyone willing to believe", asks Sonneborn (1951), ''that, if all 

 such self-duplicating components of the cell were thrown together 

 in a test tube in the proper portions with adequate food for their 

 multiplication, a Chilomonas cell or any cell at all would result? " 

 Something more seems to be needed and this is a cortical pattern 

 factor itself having genetic continuity. 



In Stentor, development is organized because there is always a 



