a number of workers, including both Darlington and Ris, but there are 

 many reasons for believing that it does actually exist and even that it is 

 bounded by a membrane or interface. 



Figure 4-12. (a) Somatic Chromosome at Anaphase: (1) kinetochore; 

 (2) matrix; (3) chromonema; (4) secondary constriction, (b) Meiotic 

 Chromosome at Diakinesis: (1) kinetochore; (2) matrix; (3) chromonema; 

 (4) chiasma. (From Wilson, G. B., 1952. "Outline of Genetics," Michigan 

 State University Press, East Lansing, Mich., Fig. 1, p. 4.) 



Numerous attempts to analyze the nucleus, and thus the chromosomes, 

 chemically have been made since Miescher's pioneering work in that 

 direction in the 1870's. Although considerable progress has been made 

 in recent years through the application of spectrophotometric methods, 

 chemical analysis of both isolated nuclei and chromosomes, and cyto- 

 chemical techniques, the physiology of the chromosome is still incom- 



STRUCTURE AND FUNCTION OF THE NUCLEUS / 89 



