Role of Preformed Structure in Cell Heredity 203 



imply that this localization of the presumed material source of the 

 new mouth and gullet is the hasis for the regular appearance of these 

 structures close to the old one and for the dependence of a new oral 

 apparatus on the presence of a preexisting one. Faure-Fremiet ( 1954 i 

 refers to this confinement of the stomatogenic kinety within the oral 

 apparatus as the hasis for its "autonomization." Here then is one 

 view, hased mainly upon the normal course of fission, of why and 

 how new structures are determined by preexisting structures: a par- 

 ticular kinety determines a particular cortical structure. 



The second type of evidence comes from experimental interferences 

 with the normal situation and leads in the main to opposite conclu- 

 sions. The most extensive and intensive work has heen done on Stentor 

 (Tartar, 1961; Uhlig, 1960). Normally, only the apical end of the new 

 oral apparatus ( called the peristomial primordium, the primordium, 

 or the anlage I arises in association with a particular kinety; the 

 hasal end extends across several kineties. Thus, the peristomial 

 primordium normally arises in a definite fixed position marked hy a 

 particular kinety pattern. In pigmented species of Stentor, the kineties 

 regularly alternate with pigmented stripes. Because the latter are 

 more conspicuous, descriptions are commonly given in terms of the 

 stripes. On the midventral surface there is a zone of narrow ramifying 

 stripes flanked on the left hy broad interpolar stripes. The apical end 

 of the primordium arises on this border and the basal part within 

 the ramifying zone. 



Is this normal position of origin of the primordium due to the in- 

 herent properties of one or more kineties in that region? Nearly 60 

 years ago Stevens ( 1903 I removed the ventral half of the body of 

 Stentor, within which lay the ramifying zone, and a considerable region 

 on both sides of it, and found that the peristomial primordium was 

 nevertheless formed. This has subsequently been repeatedly con- 

 firmed. Eventually, Tartar (1956) discovered what visible physical 

 conditions were necessary for the formation of the peristomial pri- 

 mordium. The pigment stripes in the ramifying zone are the nar- 

 rowest on the body. Around the body to the right from this zone 

 the stripes become progressively broader; they are thus broadest 

 on the other side of the ramifying zone. Tartar showed that relo- 

 cations of body parts yielded primordia only where artificial junc- 

 tures between wide and narrow stripes were made. For example, when 

 the ventral half of the body is removed, the cut edges of the dorsal 

 half join, making a new juncture between narrow and wide stripes, 

 and there a primordium arises and develops. 



Experiments such as this — and many variations of it have been 



