134 ZOOLOGY 



distinct from the second (cytologically) has permitted the observers 

 to study them more minutely and it is now possible to distinguish 

 definitely between the second and third chromosomes and so 

 establish cytologically translocations between the second and third. 

 " Chromosome II contains more chromatin than III and typically 

 appears as longer, or, when relatively condensed, thicker. How- 



c I X- 



D 

 Fig. 61. — Chromosome figures from Drosophila to show translocation 

 (B and C) and deletion (D). A represents normal condition. 

 Roman figures refer to the number of the chromosome pair, 

 X and Y to the sex-chromosomes ; XX is the " added X " 

 condition and X- indicates deletion. The dotted lines show 

 the probable translocations (from Painter and Muller (103) ). 



ever, it is not always possible to distinguish between the two 

 because these studies also show that the rate at which the chromo- 

 somes of different pairs in a given cell contract is subject to a good 

 deal of individual variation " (88). 



Fragments have been found to be detached from any one of 

 the X, II and III (88, 103), and Y (119) chromosomes, and they 

 may be attached to any of the other (non-homologous) chromo- 



