THE LIVING MACHINE BUILDING FACTORS. 149 



the plant that multiplies by buds or the unicellu- 

 lar animal that simply divides into two equal 

 parts, or the larger animal that multiplies by 

 eggs, we find that in all cases the fundamental 

 feature of the process is divisio.n. 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 founda- 

 tion of reproduction is thus in all cases cell 

 division. Now, this process of division is depen- 

 dent upon the properties of the cell. Firstly, it is 

 a result of the assimilative powers of the cell, for 

 only through assimilation can the cell increase in 

 size, and only as it increases in size can it gain 

 sustenance for cell division. Secondly, it is de- 

 pendent, 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 ani- 

 mals and plants. We can not, therefore, find any 

 explanation of reproduction until we have ex- 

 plained the mechanism of the cell. The funda- 

 mental 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 



