Genie and Non-genic Parts of the Chromosome 65 



Bauer and Beermann (1952) have described a similar case in the 

 chironomid group Orthocladiinae, though the details are somewhat 

 different. Thus the gallflies do not stand alone. 



In the same category, though the details are not so concise and 

 regular as in the typical chromatin diminution, are the facts concern- 

 ing the supernumerary chromosomes in plant cells. (For details see 

 Darlington and Upcott, 1941; Darlington and Thomas, 1941; Resende, 

 1945.) These small, centromereless chromosomes are frequently found 

 in pollen cells in different, not constant, sometimes large numbers. 



Fig. 8. Giardina ring ( heterochromatin ) in ovogenesis of Dyticus and its 

 retention in ovocyte in divisions separating egg and follicle cells. Note its mass 

 compared with that of small chromosomes. (Combined from Giardina, Giinthert, 

 and Korschelt. ) 



Theoretically, they should disappear after many mitoses, as they are 

 passively distributed in the cytoplasm during division. Actually they 

 remain, as a whole, rather constant and even accumulate in the cells 

 of the germinal layer, which may be compared to a germ track. It is 

 generally recognized that these supernumerary chromosomes are 

 heterochromatic. Obviously they take some active part in divisions in 

 spite of the absence of the centromere, as otherwise they could not 

 keep their own in the germ cells. This must amount to some control 

 of their movements by a differentiated cytoplasm. I think that the 

 most remarkable fact found thus far is Darlington and Thomas' (1941) 



