14 Vertebrate Embryology 



mother's father, nor the characters of any of 

 its father's ancestors. 



Delage and Herouard have elaborated a 

 theory that is, briefly, as follows : The simplest 

 organisms are capable of reproducing them- 

 selves indefinitely by a process of repeated 

 division. More highly organized beings are 

 not possessed of this indefinite power of di- 

 vision, and must occasionally undergo a process 

 of fusion or conjugation. This process con- 

 sists of two parts, the elimination of chromatic 

 material (maturation), and the conjugation 

 proper, or fertilization. The maturation is usu- 

 ally considered as an accessory phenomenon, 

 whose object is simply to make the fertiliza- 

 tion possible, but, according to this hypothesis, 

 " The essential phenomenon is the chromatic 

 reduction, and the fecundation is an addition 

 which is advantageous but not indispensable." 



In the simplest organisms metabolism is a 

 closed cycle ; but in more complicated beings 

 this is not the case, and there is gradually 

 accumulated a substance which is injurious 

 and which affects all the functions of life, 

 especially those concerned in cell division. 

 Unless this substance is gotten rid of, the cell 

 will die. 



