THE LAW OF BIOGENESIS 75 



is shown. The nucleus is larger and the cyto- 

 plasm has increased greatly. The cell is still a 

 unit and the only change is an increase in size in 

 the two parts of the cell. But how did these parts 

 come to grow in this fashion? 



Only a partial answer can be made to such a 

 question. Much of this growth consists in the 

 accumulation of food energy. The body of the 

 animal furnishes the necessary amount of food 

 which, on reaching the egg cells that are to grow 

 to maturity in a given reproductive cycle, is 

 elaborated into living egg-protoplasm. This 

 energy is stored in the cytoplasm and is one of the 

 earliest instances of preparedness on record. 



The next three figures, 20-21-22, introduce us 

 to a technical phase of reproduction but one neces- 

 sary to the discussion if we are to have any com- 

 prehension of the modern problem. In the nu- 

 cleus of all cells is found a complicated structure 

 that undergoes various changes. This substance 

 is given two different names which are to be re- 

 garded as descriptive terms for the same substance 

 at different stages of activity, i'hese two terms 

 are chromatin and chromosomes. In Fig. 18 

 the nucleus has scattered granules with no constant 

 arrangement. Each of these granules takes a 

 certain kind of stain or dye when prepared for 

 study. Such granules are termed chromatin 

 granules. When a number of nuclei are studied. 



