V 



Ferfilizedl egg cell 



> y^ Epithelial 



cells of pancreas 



(filiated tracie^ 



Cardlage cells 



THE DIFFERENTIATION OF CELLS 



In the earliest stages of an individual's development all the cells are very much 

 alike. When there are several hundred cells, it is possible to make out layers of 

 distinct kinds of cells. Later we can recognize different tissues, or masses of similar 

 cells, such as skin, muscle, bone. After the distinct tissues are established, a dividing 

 cell produces new cells like itself 



