THE INTERPHASE NUCLEUS 



the areas of nuclei from different tissues in tetraploid and diploid 

 strains, and found considerable deviation from a 2:1 relationship. 

 Moreover these aberrant ratios themselves vary from tissue to tissue. 

 Barigozzi^^^ measured nuclear areas in epithelial cells of the gut of an 

 octoploid race of Artemia and found the range of variation to be nearly 

 fourfold. It is clear that factors other than their content of chromosomes 

 can affect the size of interphase nuclei. Barigozzi suggested that some 

 of these may be hereditary, for he found much less variation in nuclear 

 size between mother and sister individuals in the octoploid Artemias. 

 Thus in polyploid individuals, in every cell of which there is the same 

 multiple of the haploid number of chromosomes, measurement of 

 nuclear size alone is not always a sufficient guide in deciding the value 



Figure 17 Relative nuclear areas of epidermal 

 nuclei in polyploid amphibia, for each degree of 

 ploidy. Plotted from the data of Fankhauser 

 and HuMPHREY^^* and Fankhauser. ^83 (circles, 

 Triturus; dots, Ambystoma. Where given, the 

 range and the mean of each degree are indicated. 



of this multiple. Bowen^^^ and Schrader^^^ have shown that in the 

 Bug Arvelius albopunctatus the size of the spermatocyte nuclei in different 

 lobes of the testis may vary by as much as 4:1, yet in all these cells the 

 chromosomes which appear in the subsequent stages of meiosis are 

 similar in size and number (Figure 18)*. In Amphibia, Beatty and 

 FiscHBERG^^^ state that 'large significant differences in mean nuclear 

 size can be found between diploid frog tadpoles, even of the same 

 batch'. It follows, therefore, that where the degree of heteroploidy is not 

 constant in the various cells and tissues of a single individual, statistics 

 of nuclear dimensions must be interpreted with reserve. 



•ScHRADER and Leuchtenberger^*''^ have shown that the DNA content of Arvelius 

 spermatocytes of different sizes is approximately constant, but that their content of RNA 

 and protein is proportional to their size. 



55 



