THE MITOTIC CYCLE 



process which Geitler^'" first described as 'endomitosis', which takes 

 place within an intact nuclear membrane. This is especially character- 

 istic of insect tissues in which histological differentiation is accompanied 

 by increase in nuclear size. In the pond skater Gerris lateralis the degree 





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Figure 59 Endomitosis in the ovarian nurse cells oi Drosophila melanogaster. Upper 

 row: a reticular, an early, and a late prophase (not all elements shown). 

 Middle row: similar sequence of changes, association of chromatids looser 

 in late prophase. Lx)wer row: details of largest nuclei. Many hundred 

 chromosomes must be present in the felt-like aggregations seen in the lower 

 right figure. From Painter^"* {By courtesy, J. Roy. micr. Soc). 



of polyploidy in such large nuclei in interphase is indicated by the num- 

 ber of heterochromatic X-chromosomes (Geitler;^'! Figure 58). During 

 prophase these nuclei contain bundles of chromosome threads which are 

 inferred to be undergoing reduphcation. In the nurse cells of the ovary 

 o^Drosophila (Painter and Reindorp^'^^) the homologous chromosomes 

 are closely associated (Figure 59), a condition which seems to be another 



150 



