EXPLANATION OF PLATES 



All figures were first drawn with the aid of a camera lucida. Except when 

 otherwise stated, the magnification of the original drawings was 1630 diameters. 

 These were then enlarged two diameters and finished with careful reference to the 

 object. They were reduced one-half in reproduction. Although it is difficult to 

 draw accurately such small objects as fish chromosomes, all possible care has been 

 taken to preserve their true proportions. 



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