ORIGIN AND DEVELOPMENT 45 



twenty, but half are now maternal and half 

 are paternal. This is believed to be the 

 physical basis of heredity, as it is assumed 

 that hereditary characteristics are conveyed by 

 the chromosomes. This statement implies that 

 hereditary matter has been transmitted not 

 from parents only but from grandparents and 

 possibly from individuals of many previous 

 generations. 



17. The fecundated ovum then divides 

 into two, each of the two into four, and so on 

 until a large number of cells are formed and 

 by a remarkable series of processes, known as 

 Karyokinesis, each cell, when it divides, 

 transmits to its two descendants exactly the 

 same number of chromosomes, one half 

 representing the male while the other half 

 represents the female side. Thus, according to 

 modern theory, every cell in the body may possess 

 hereditary characteristics. 



18. The early cells form certain layers from 

 which all the organs and tissues of the body 

 are developed. 



The early embryonic tissue in which the 

 future being is formed is composed of two 



