THE CHROMOSOMES 



119 



somes again become visible, preparatory to the next 

 division, it has been found by Boveri in Ascaris, 

 which is particularly well suited for the study of this 

 point, that in sister cells the configuration of the 

 groups of chromosomes is the same (Fig. 41). The 

 similarity of the sister cells would be expected had 

 the chromosomes retained during the resting stage 

 the same shape and size and relative location that 

 they had at the end of the last division. On no other 



a 



d 



Fig. 41. — Four pairs of sister cells of Ascaris, in which the chromo- 

 somes are reappearing. Note the similarity of arrangement in the cells 

 of each pair. (After Boveri.) 



view can we so readily understand the similarities 

 between the sister cells; for, in other cells of these 

 same embryos that are not sister cells, a great variety 

 of arrangements is found, and no two arrangements 

 are so nearly alike as are those that are found in 

 cells that have separated from each other at the last 

 division. In a few instances certain observers be- 

 lieve that they have even been able to distinguish 

 the separate chromosomes throughout the whole 



