THE MITOTIC CYCLE 



of the salivary nucleus in Chironomus. Bogojawlensky^^^ finds that in the 

 development of the Anopheles larva, giant chromosomes are not seen in 

 any tissue until the fourth of a series of nuclear size classes has been 

 attained. Painter and Reindorp^^^ find that the nurse cells of the 

 Drosophila ovary undergo a discontinuous increase in size by means of 

 successive cycles of endomitosis (Figure 59). 



The only investigations on the relationship between chromosomal 

 and nuclear size in vertebrate tissues are those of Biesele et alii. Their 



'^ 05 

 6 



a 

 10 

 12 

 n 



16 



11 



06 0-7 08 0-9 10 



Average chromosome volume 

 in n 



12 13 IV 15 16 17 



78^ 



Figure 24 Histograms showing distribution of chromosomal 



volumes in nuclei of the rat liver (a) normal, and (b) during 



regeneration. Plotted from data given by Biesele. 2^' 



results suggest a clear distinction between growth in a normal tissue 

 such as the regenerating liver (Biesele^^o) and in some tumours, for 

 whereas the same distribution of chromosomal size is found in both 

 diploid and polyploid cells, of the normal and the regenerating liver 

 (Figure 24), chromosomes of double the usual size were found in tu- 

 mours of a goldfish (BiESELE^is)^ of the mouse (Biesele et alii^^^), and 



62 



