The Chromosome and Its Division 1 1 



rather enigmatic diflFuse centromere which Schrader (1953) finds in 

 coccids and scorpions. Since this would mean a stretching of the 

 centromere the entire length of the chromosome, it would exclude any 

 relation to the series of chromomeres in the chromonema and demand 

 a self-duplication which occurs completely in harmony with the 

 processes for the entire chromosome. However, the possibility cannot 

 be excluded that the diffuse centromere is a repeating member of the 

 chromomeric series, pushed together in the metaphase chromosome by 

 the extreme coiling. 



This leads us to Lwoff's and Chatton's brilliant studies and 

 generalizations based upon the division of the infusorian body (see 

 Lwoff, 1950^). The equivalent of a centriole in a dividing cell or in a 

 flagellate or sperm and, therefore, of a centromere is, in Infusoria, 

 a kinetosome. This body can produce different structures according to 

 its position in the cell or the time within the life cycle. It can divide 

 into two kinetosomes; it can sprout a fiber or a cilium; it can grow into 

 a trichocyst, a tubular structure which can be protruded; also a 

 trichite, a stiff hair. The decisive feature is that the kinetosome cannot 

 be formed de novo, but is a self-duplicating elementary structure. 

 This means that a new kinetosome cannot be produced without the 

 participation of the old one, serving as a template or autocatalytic 

 agent. In this respect the kinetosome would be comparable to the 

 genie material, but it should be emphasized, in view of Watson and 

 Crick's work on the template structure of the DNA molecule, that no 

 nucleic acid is present in these structures, just as there is none in 

 centrioles and centromeres. The comparison could also be extended to 

 the kinetosome's ability to produce the forementioned products de- 

 pendent upon its chemical surroundings and to change its func- 

 tions by "mutation." One important point must be added, or, rather, 

 specified. When a kinetosome divides and one of the products develops 

 irreversibly into a trichocyst, this may be called an unequal division. 

 However, it may also happen that one of the products of unequal 

 division does not transform directly into a trichocyst, but first divides 

 repeatedly before each descendant becomes a trichocyst. 



As aheady stated, there is every reason to assume that the cen- 

 tromere in the chromosome is equivalent to the centriole and also to 

 the kinetosome. Thus it may be concluded, on the basis of Lwoff's 

 analysis, that the centromere is basically a self-duplicating body just 

 as any genie material within the chromosome or any self-duplicating 

 material within the cytoplasm. Compared with the kinetosome, how- 

 ever, the potencies of the centromere are limited to the formation ( or 



