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Fig. 7. — Diagram of Chromosome Forms at Mitosis. 



Metaphase chromosomes of plants and animals represented uniformly with 

 the same diameter and with the two chromatids in the same line of vision at 

 the constrictions, which are therefore represented by single threads. This is 

 only constantly the case with polar views of the centric constriction : in side 

 views of this constriction the connection is double, the chromatids being seen 

 side by side ; in polar or side views of secondary constrictions the connection is 

 double or single according to the chance arrangement, 



I. Chromosomes with a single centric constriction. 



A. " Terminal " (with one arm too small to be seen as a rule), e.g., Steno- 

 bothrus lineatus (Janssens, 1924 ; Belar, 1928), Drosophila melanogaster , 

 X-chromosome (Stern, 1929), Sphcsromyxa sabrazesi (Belar, 1926 b). 



B. " Terminal," short chromosome, e.g., Drosophila melanogaster fourth 

 chromosome (Stern, 1929), Yticca filamentosa (Taylor, 1925 b). Many 



