182 ROBERT T. HANCE 



somes and proceeding down the series. In row 6 a 41-chromosome 

 cell is represented. Here the first two chromosomes are very 

 clearly entire, judging their lengths by those of the first two 

 chromosomes of row 1. It appears very probable that either 

 chromosome 3 or 4 has been the one to lose the portion repre- 

 sented by chromosome 41. In row 11 the first two chromosomes 

 are long, but so, also, are the other chromosomes in this cell, 

 and when considered from this point of view these chromosomes 

 are relatively very nearly as short as the first pair in row 10. 

 The chromosomes in row 11 measure 176.1 cm., while the total 

 length of those in row 16 is 153.6 cm. Row 11 is therefore 8.8 

 per cent longer than row 10. If the total lengths of the chro- 

 mosomes vary by 8.8 per cent then, according to the state- 

 ments made above that in reduction (for whatever reason) 

 each chromosome suffers proportionately, any corresponding 

 pairs from either of the cells should differ by very nearly the 

 same amount. It is, of course, not expected that exact results 

 may be obtained in all cases for reasons pointed out earlier. 

 Consider for example the pairs composed of chromosomes 1 

 and 2 in rows 10 and 11. These chromosomes average 5.1 cm. 

 in length in row 10 and 6.7 cm. in row 11. and consequently 

 differ by 7.6 per cent. In this instance there is a discrepancy 

 of 1.2 per cent. When the next pair in each cell is compared 

 it is found that the difference is 8.8 per cent exactly the same 

 as the variation between the total lengths. This is sufficient, 

 I think, to indicate that the difference in total length is due to a 

 proportional reduction of the chromosomes of row 10 and that 

 the corresponding pairs in each of the rows are comparable. 

 Furthermore it is evident that the longer chromosomes in both 

 rows have in all probability lost a portion of their length since 

 they are shorter than the corresponding ' typical' pairs. 



The fact that it is the members of the long end of the chromo- 

 some series which are breaking down becomes more evident in 

 text figure 3. For the sake of clearness the graphs for only 

 three greatly fragmented cells have been drawn. These are 

 represented in light unbroken lines. Note that in all three 

 cases the curves start out below the curves representing the 



