178 



ROBERT T. HANCE 



spermatogonia. The measurements given above bear this out. 

 It may be pointed out that, although considerable variation exists 

 between the total lengths of all of the chromosomes in the 

 various cells, this variation is not greater in one tissue than 

 in another and falls within the limits determined for the sperma- 

 togonia. 



On plate 10 the chromosomes of a number of cells in various 

 degrees of fragmentation are arranged according to size. It is 

 obvious that the somatic chromosomes, particularly at the long 

 end of the series, are shorter than those in the same column in 

 the row devoted to the spermatogonia! chromosomes or to the 

 somatic cells possessing forty chromosomes. The conditions 

 illustrated on this plate will be referred to later. 



Table of total chromosome lengths in the cells of various tissues and in cells possessing 

 different numbers of chromosomes 



Amnion. . . 



Blood 



Brain 



Brain 



Brain 



Brain 



Limb bud. 



Liver 



Lung 



IVIyotome. 



NUMBER OP 

 CHROMOSOMES 



41 

 55 

 40 

 45 

 50 

 56 

 52 

 53 

 55 

 43 



TOTAL LENGTH OF 



CHROMOSOMES IN 



CENTIMETERS 



129.2 

 129.8 

 143.9 

 124.1 

 117.0 

 139.9 

 152.6 

 158.4 

 176. 1 



Average 



139.3 



The length of the chroinosome fragments. In my studies on 

 Oenothera scintillans I considered all the chromosomes which, 

 when arranged according to length, fell below the shortest 

 chromosome in the normal diploid series, to be portions or 

 fragments of longer chromosomes and I found them to be re- 

 markably alike in length. When the chromosomes on plate 9, 

 to the right of chromosome 40, are studied, it is evident that 

 they, too, vary but little. By actual measurements they aver- 



