30 SCIENCE AND PHILOSOPHY OF THE ORGANISM 



A certain number of pairs of small threads, the so-called 

 " chromosomes," are the ultimate result of this process, 

 which intentionally has been described a little schematically, 

 the breaking and the splitting in fact going on simul- 

 taneously or occasionally even in reverse order. While 

 what we have described is performing in the nucleus, there 

 have happened some typical modifications in protoplasm, and 

 then, by an interaction of protoplasmatic and nuclear factors, 

 the first step in the actual division of the cell begins. Of 

 each pair of the small threads of chromatin one constituent 

 is moved to one side of the cell, one to the other ; two 

 daughter-nuclei are formed in this way ; the protoplasm 

 itself at the same time forms a circular furrow between them ; 

 the furrow gets deeper and deeper ; at last it cuts the cell 

 in two, and the division of the cell is accomplished. 



Not only is the growth of the already typically formed 

 organism carried out by a series of cell-divisions, but also 

 development proper in our sense, as a " production of visible 

 manifoldness," is realised to a great extent by the aid of 

 such divisions, which therefore may indeed be said to be of 

 very fundamental importance (Fig. 1). 



Each cell-division which promotes growth is followed by 

 the enlargement of the two daughter-cells which result from 

 it ; these two daughter-elements attain the exact size of the 

 mother-cell before division, and as soon as this size is reached 

 a new division begins : so the growth of the whole is in 

 the main the result of the growth of the elements. Cell- 

 divisions during real organ-formation may behave differently, 

 as will be described at a proper occasion. 



