THE CHROMOSOMES 75 



network. The network resolves itself into a definite 

 number of threads or rods at each division of the cell 

 {fig. 30). These rods we call chromosomes. Each- 

 species of animals and plants possesses a character- 

 istic number of chromosomes which have a definite 

 size, and sometimes a specific shape, and even char- 

 acteristic granules at different levels. Beyond this 

 point our strongest microscopes fail to penetrate. 











*A *v~. « 







Fig. 30. — Diagram, slightly modified from Agar, to show a 

 ty])ic'al cell division (lvaryo]<inesis). The chromosomes are 

 represented as black threads and rods, which pass onto the 

 spindle fil)res and then move to the poles of the spindle where 

 they sul)sequently ])ecome vacuolated to form the resting nuclei 

 of the two daughter cells. 



