Genie Control of Development 303 



could produce the gradient are the oral zone and its kinetosomes, 

 which control its morphogenesis. Actually, in Blepharisnm, anterior 

 and posterior special kinetosomes exist, and here it is the mid-nodules 

 which decline. When anterior nuclear nodes were transplanted in 

 Stent or into a posterior position and in Blepharisma into a mid-posi- 

 tion, they started to show the typical decline. 



The relation between kinetosomes and macronucleus may be 

 stated in another way by comparing the effect of "declining" nodules. 

 At a definite level of inactivation, the posterior nodules in Stentor 

 cannot support the differentiation of the stomatic organs except that of 

 the ordinary cilia (which do not grow without a macronucleus). In 

 another experiment, partially inactivated nodes suflBce for the mainte- 

 nance of some peristomal structures but not for a gullet and the 

 geometric alignment of the peristome. Thus it is concluded that the 

 subnuclei exist in as many different morphogenetic states as there are 

 possible levels of kinetosomic function. 



Weisz thinks that such facts may be explained by the assumption 

 that subnuclei lacking one function of morphogenesis ( or another one ) 

 lack the genes or the gene products needed. Thus nodal inactivation 

 may be considered to be the expression of progressive and differential 

 inactivation of genes comparable to the assumed parallel processes in 

 the development of Metazoa. An alternative is that the consecutive 

 states of the subnuclei are an expression of a quantitative phenome- 

 non, for example, differential activity of the whole genome which 

 might result in a lowering of quantity or potency of a nuclear product. 

 (This would, of course, involve different thresholds of action for the 

 different affected fields. Though 'not stated in this form, this is ob- 

 viously in Weisz' mind.) 



Weisz thinks that the second alternative is the correct solution, 

 including an interaction between nuclear and kinetosomal products. 

 This means that origin-specific products of the higher types of more 

 important kinetosomes keep up the nuclear activity at the necessary 

 high level. This concept is used to explain the above-described inac- 

 tivation of the posterior nodules. He assumes that soon after fission 

 the anterior nodules receive the largest share of the kinetosomal sub- 

 stance, which gives them an initial advantage in the competition for 

 the substance. When the substance becomes short in supply, the 

 posterior nodules first feel the pinch. In detail, then, the relative ac- 

 tions of the macronucleus and the kinetosomes is based upon the need 

 of the autonomous kinetosomes for proper endoplasmic substances 

 as substrates for differentiative syntheses. This might mean that the 



