Experimental Transformation of Species 



Fig. 66. The Chromosomes in Cell Division 



In the resting stage, A, chromosomes are not distinguishable. Activity begins by 

 the chromatin material taking form and the centrosome at the side of the nucleus di- 

 viding into two, B. The centrosomes start moving toward opposite poles, C, while the 

 chromatin fiber breaks up into a definite number of chromosomes (six pairs in the 

 diagram). The chromosomes appear to be attached to the " spindle fibres " connected 

 with the centrosomes, D, and the nuclear membrane disappears. The chromosomes 

 arrange themselves in pairs about the equatorial plane, £, the centrosomes occupying 

 opposite poles. The two chromosomes of each pair move toward opposite poles, jF. 

 The chromosomes in the two opposite groups fuse together, G; and two new nuclei 

 are constituted, H. (Adapted from Agar's Cytology, copyright by Macmillan & 

 Company, Ltd.; from Babcock and Clausen, Genetics in Relation to Agriculture, 

 published by McGraw-Hill Book Company.) 



