202 The Nature of Biological Diversity 



into a unit of cortical structure, the ciliary corpuscle, which develops 

 kinetosomes and other parts. Definite proof or exclusion of one or 

 the other view is still lacking. 



This uncertainty about the self-reproduction of kinetosomes has 

 obvious but limited implications for the genetics of cortical organiza- 

 tion. The structures and processes with which we are concerned are 

 at higher levels than that of kinetosomes and the way they arise. They 

 include the ways in which kinetosomes are grouped in more complex 

 structures, as well as the seemingly simpler creation of fields with 

 characteristically positioned and oriented kinetics. The problem of 

 the origin, development, and inheritance of structure at this level is 

 independent of the answer to the question of the origin and produc- 

 tion of individual kinetosomes. 



The morphogenetic aspects of the kinetosome theory are far more 

 important for present purposes. Local differences in cortical structure 

 in other ciliates, as in Paramecium, involve variations in the spacing, 

 orientation, differentiation, and relative growth rates of kinetics and 

 groups of kinetosomes. It is therefore of basic importance to know 

 whether such variations are inherent in the constituent kinetosomes 

 and kineties or whether they are imposed upon them by other features 

 of the local milieu. On the choice between these alternatives, the 

 kinetosome theory is not firm. Lwoff (1950) recognized both of them 

 and seemed to favor the latter. In other words, he thought it to be 

 more likely that the kinetosomes and kineties were indispensable in- 

 struments of cortical differentiation, rather than that they might be 

 the cause of it. Others have come out strongly for the causal interpre- 

 tation (Wiesz, 1951 ). Faure-Fremiet (1945-1954) repeatedly considers 

 the possibilities in varied lights; he sometimes seems to lean toward 

 the one, sometimes toward the other interpretation. Because the choice 

 between these alternatives is fundamental for our theme, the main 

 types of evidence bearing on it will now be considered. 



The first type of evidence comes from observations of the normal 

 course of events. Any particular structure normally arises at a partic- 

 ular spot marked either by a certain pattern of kineties or by asso- 

 ciation with the same kinety. This is well illustrated by the normally 

 constant locus of origin of a new oral apparatus. As the most promi- 

 nent set of cortical structures, it has been studied most. In many 

 ciliates, such as Tetrahymena, it always arises in association with a 

 particular interpolar kinety designated as kinety No. 1 or the "sto- 

 matogenic" kinety. In Paramecium, the endoral kinety (page 170), 

 by the right edge of the mouth, is held by some to be the stomatogenic 

 kinety (Roque, 1956b; Porter, 1960, at least in part). Their views 



