GROWTH AND REPRODUCTION 783 



It will be seen that we are still far from understanding the circum- 

 stances which lead to the determination of sex. In some cases it is 

 apparently due to an initial difference in metabolic rhythm, in others 

 to a predetermined morphological difference in the sex units. 



Death. Death is the total cessation of the cell activities of the 

 individual. Cells are always dying and being replaced within the 

 individual. After a time, however, either by the process of decay 

 following a natural adolescence and maturity, or more often as the 

 result of disease or accident, one of the vital functions fails, the 

 general metabolism of the body ceases to be efficient, and death 

 ensues. The custodianship of the genetic by the somatic cells is 

 finished. Yet, if the former have fulfilled their function, the 

 individual does not wholly die; life continues in the offspring. On 

 death, there is a transformation, but no destruction of energy. 

 The disintegrating cells pass into materials of lesser complexity, 

 some or all of which are again worked up into the complex forma- 

 tions of life. Thus continues the ceaseless life and death cycle of 

 the ages. 



