222 WHAT IS LIFE 



the ovum gives rise to a new individual; otherwise 

 it soon dies. 



To repeat : FertiHzation, conception, having taken 

 place, immediately the process of cell division com- 

 mences. With the first division of the impregnated 

 ovum, the growth and development of the new in- 

 dividual is begun. Conception, fertilization, once 

 having taken place (in normal fertilization that 

 means when the spermatozoon has entered the egg), 

 the egg passes into an irreversible condition. It may 

 die, but if it does, it is the incipient new individual 

 that dies. An unfertilized egg is a potential new 

 individual; a fertilized egg is actually a new in- 

 dividual in its initial stage of existence. The be- 

 ginning of the new individual dates from the moment 

 of conception. {See p. 164.) 



The mother supplies everything for the embryo 

 but a single cell, the microscopic germ-cell supplied 

 by the father in the fertilization of the ovum. Up to 

 birth, the embryo is vegetal in its mode of obtaining 

 nourishment: at an early stage what may be de- 

 scribed as a stem-root of the embryo buries itself in 

 the food supply of the egg or the placenta of the 

 maternal organ. 



This in fewest words outlines the process of sexual 

 reproduction. 



It is necessary now to note more closely the re- 



