74 EVOLUTION AND GENETICS 



organism. They found that organs such as the 

 brain, the heart, the hver, the lungs, the kidneys, 

 etc., are not themselves the units of structure, but 

 that all these organs can be reduced to a simpler 

 unit that repeats itself a thousand-fold in every or- 

 gan. We call this unit a cell. 



The egg is a cell, and the spermatozoon is a cell. 

 Fertilization is the union of two cells. Simple as the 

 process of fertilization appears to us today, its dis- 

 covery swept aside a vast amount of mystical specu- 

 lation concerning the role of the male and of the 

 female in the act of procreation. 



Within the cell a new microcosm was revealed. 

 Every cell was found to contain a spherical body 

 called the nucleus {fig. 29). Within the nucleus is 

 a network of fibres ; a sa^) fills the interstices of the 



Fig. 29.— Diagram of a "typical cell," 

 showing cell-wall, cytoplasm (with solid 

 and fluid inclusions) and centrosome 

 witli astral rays (doubtfully present in 

 resting stage). In the center is the 

 nucleus with its network of chromatin, 

 and its nuclear sap. 



