GENETICS OF HETEROMORPHIC CHROMOSOMES 463 



seen in text figure A where the longer arms of both homologues 

 are free. This is one of the clearest instances with which I am 

 famiUar where either the long or short ends of a given atelomitic 

 tetrad become free. Wenrich ('17, p. 488) has noted and dis- 

 cussed variation in method of transformation of certain tetrads 

 in another species. I can only agree with his conclusion that 

 chromatid movements cease at a certain stage of the prophase 

 and are not resumed until the metaphase. The movements of 

 the chromatids during the early prophase have considerable 

 range of variation, consequently any particular tetrad may enter 

 the metaphase in a number of forms as will be evident to any one 

 who cares to examine critically the four largest tetrads in the 

 appended plates. While any two of these chromosomes might 



{^Mll 



Text fig. A Drawings of tetrad no. 7, showing the various forms in which 

 it has been found. Four individuals represented. 1 and 2, the typical short- 

 armed form which occasionally opens in the same specimen with the long arms 

 free; 3 and 4, shows the same condition in an individual in which there has been 

 a secondary shift of point of fiber attachment on one homologue; 5, very rare 

 telomitic form; 6, heteromorphic form. 



be interchanged in their position in the size series, none of these 

 four would be confused with the other chromosomes of the com- 

 plex, except with number 8 in the two individuals where it is atelo- 

 mitic (rows 18 and 24). In the complexes represented in rows 

 12 and 17 all four are axial rings which are very similar in appear- 

 ance, whereas the same four chromosomes occur in a variety of 

 forms throughout the plates. 



We will consider only one modification — the E-shaped tetrads. 

 Those familiar with first spermatocyte prophase conditions know 

 that the larger chromosomes usually form double or triple rings at 

 this stage, each successive loop being at a right angle to the pre- 

 ceding one (Sutton, '02) . Such tetrads frequently . enter the 

 metaphase in corresponding forms with rings at angles to each 



