152 THE CHROMOSOMES 
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 
@ b c 
Fic. 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.) 
d 
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 
