Genie and Non-genic Parts of the Chromosome 73 



somes indicate the absence of the heterochromatic regions. It is 

 irrelevant for the present discussion that the big block in the 

 X-chromosome is represented in the salivaries by a single band, which 

 might mean that a tiny euchromatic section is present in the block 



Fig. 10. Different prophases of neurocytes of Drosophila virilis larvae, showing 

 large amount of heterochromatin in heteropyknosis in form of chromocenters or 

 individual blocks. (From Makino. ) 



(Muller's description of this band as a gene which organizes the 

 heterochromatic block does not appeal to me; it actually seems 

 dangerous, because it suggests an explanation while being only a way 

 of terminology). It has been claimed (Prokofyeva, 1935) that within 

 the chromocenter the Y-chromosome can stiU be recognized as a few 



