196 The Nature of Biological Diversity 



right and left kinety fields. Normally, this juxtaposition is on the post- 

 oral suture, but when two oral meridians are not more than 90° 

 apart, a third juxtaposition with reversed right-left relations exists 

 between them, and there a third cytopyge arises, in the absence of a 

 third oral segment or any part of it (page 182). This suggests that 

 cytopyge formation is determined by interaction between these two 

 kinety fields or the cortical regions in which they are located. 



This, together with analyses in other ciliates to be discussed later, 

 makes more credible the possibility considered above in relation to 

 the consequences of "natural grafts," of de novo origin of the oral 

 apparatus by results of interaction between other juxtaposed diverse 

 kinety fields or cortical regions. Ehret and Powers ( 1959 ) have also 

 pointed out this possibility. Indeed, virtually the whole oral meridian 

 from pole to pole, as well as the juncture between vestibule and 

 gullet, is a series of junctures between visibly diverse cortical pat- 

 terns, which would be more than ample to account in principle for 

 all the determinative actions in morphogenesis and cell heredity 

 correlated with the oral segment and its parts, if indeed such actions 

 are the essential ones involved. 



In the light of the preceding account, a preliminary summarization 

 of the main relations may be attempted. In general, new oral segments 

 are formed where and only where oral segments or their decisive 

 correlated cortical pattern junctures preexist. The rudiment of a new 

 oral apparatus likewise arises where and only where an oral apparatus 

 or its cortical determiner preexists. The preexisting oral apparatus 

 and the parts of the oral segment beside and anterior to it pass to the 

 proter, the anterior product of fission; the new rudiment and the parts 

 of the oral segment beside and posterior to it pass to the opisthe, the 

 posterior product of fission. Both proter and opisthe form new half- 

 bodies. Except for the new oral rudiment, formation of these new 

 parts involves: localized and differential (in space and time) increase 

 in the number of kinetosomes in preexisting kineties; formation of 

 the cleavage line by breaks in the kineties starting on the left at the 

 oral meridian and proceeding around the body to the oral meridian; 

 the elongation of the kineties (spacing the originally crowded kineto- 

 somes) according to a definite space-time pattern which creates the 

 new kinety fields; specific elongation of the right circumoral and 

 neighboring kineties of the developing opisthe forward into the cleav- 

 age line and to the left, so as to create a new preoral suture in the 

 opisthe from part of the cleavage line; induction of specific new 

 developments at junctures of specific cortical regions — certainly the 

 induction of a cytopyge where new posterior right and left kinety 



