176 ROBERT T. HANCE 



As a constant relationship between chromosome pairs had been 

 found in Oenothera scintillans, it was of interest to determine 

 whether such exists in the pig. That it does is shown in the 

 above table in the column to the right. There the relationship 

 of the pairs is expressed in terms of per cent, i.e., a shorter pair 

 is a certain per cent of the length of the next longer pair, etc. 

 There is a rather large increase in this percentage relationship 

 at either end of the series. These relationships will be more 

 readily understood from text figure 4 when the heavy black band 

 expresses the percentage of difference between pairs of chromo- 

 somes in the spermatogonia, drawn from the figures given above. 

 This curve shows a remarkably uniform difference in length 

 between the pairs, except at the two extremities. In cells in 

 which the total length of the chromosomes is short, all of these 

 have been affected equally in the size reduction, as the per- 

 centage relationship between the pairs is the same as between 

 the same pairs of the ' longer' cells. 



Somatic cells 



Total lengths of the chromosomes. The total lengths of the 

 somatic chromosomes in the various tissues is given in the fol- 

 lowing table. As can be seen, the total lengths of the chromo- 

 somes in the somatic cells falls within the limits determined for 

 the spermatogonia. The one exception to this statement — the 

 fifty-chromosome brain cell measuring 117 centimeters — falls 

 below the minimum length found for the spermatogonia by such 

 a small amount that I am not inclined to attach any importance 

 to it. The average length of the various cells given above is 

 139.3 centimeters, which is exceedingly close to the average 

 found for the germ cells, 136.9 centimeters. The lengths from 

 various cells are compared with those of the spermatogonia in 

 text figure 2. It is evident that, since the total length of the 

 chromosomes in the various classes of cells is approximately the 

 same, the increased number of chromosomes must be due to 

 fragmentation. 



Figures 23 ,to 80 show that any tissue may have metaphase 

 plates that vary as much in total diameter as do those of the 



