MAMMALIA 313 



basis on which it is founded, the student is asked to observe 

 that in the cell not only do the chromosomes divide, but the 

 whole of the nucleus and the cytoplasm. Moreover, the fact 

 of polarity is becoming recognised as a factor of importance. 

 Orientation is marked in the Protozoa. It is not absent in 

 the protozoon phase of the Metazoa. 



