172 THE STORY OF LIFE'S MECHANISM. 



plies by eggs, we find that in all cases the 

 fundamental feature of the process is division. 

 In all cases the organism divides into two or 

 more parts, each of which becomes in time like 

 the original. Moreover, when we trace this 

 division further we find that in all cases it is 

 to be referred back to the division of the cell, 

 such as we have described in a previous chapter. 

 The egg is a single cell which has come from the 

 parent by the division of one of the cells in the 

 body of the parent. A bud is simply a mass of 

 cells which have all arisen from the parent cells 

 by division. The foundation of reproduction is 

 thus in all cases cell division. Now, this process 

 of division is dependent upon the properties of 

 the cell. Firstly, it is a result of the assimila- 

 tive powers of the cell, for only through assimi- 

 lation can the cell increase in size, and only as it 

 increases in size can it gain sustenance for cell 

 division. Secondly, it is dependent, as we have 

 seen, upon the mechanism of the cell body, and 

 especially the nucleus and centrosome. These 

 structures regulate the cell division, and hence 

 the reproduction of all animals and plants. We 

 can not, therefore, find any explanation of repro- 

 duction until we have explained the mechanism 

 of the cell. The fundamental feature of nature's 

 machine building is thus based upon the machinery 

 of the nucleus and centrosome of the organic cell. 

 Aside from the simple fact that it preserves 

 the race, the most important feature connected 

 with this reproduction is its wonderful fruitful- 

 ness. Since it results from division, it always 

 tends to increase the offspring in geometrical 



