MYSTERY OF THE CELL 341 



After some further discussion of the views of other 

 writers, he goes on to show that the chromatin substance 

 is not only contained in the germ-cells, but also in all the 

 cells of the entire organism in each phase of its develop- 

 ment, which is effected by the constant division of the cells 

 and their nuclei, the chromatin continuing to grow during 

 the whole time. But in the body it enters on a long and 

 complex process of growth, so as to build up the substance 

 of all the varied organs and tissues, and also for the repair 

 or renovation of these various tissues as they require it. 

 He illustrates the successive changes which he supposes the 

 chromatin to bring about, and for which purpose it is so 

 accurately divided and subdivided from the very beginning, 

 in the following passage : 



"Even the two first daughter-cells (E) which result from the 

 division of the egg-cell give rise in many animals to totally different 

 parts. One of them, by continued cell-division, forms the outer 

 germinal layer, and eventually all the organs which arise from it, 

 e.g. the epidermis, central nervous system, and sensory cells; the 

 other gives rise to the inner germinal layer and the organs derived 

 from it the alimentary system, certain glands, etc. The conclusion 

 is inevitable that the chromatin determining these hereditary tend- 

 encies is different in the very first two daughter-cells." 



Later on he shows in great detail how similar but even 

 more complex changes take place in the newly fertilised 

 germ-cell in which the male and female elements are com- 

 bined, for the purpose of bringing about the accurate 

 partition of these elements in all the cells which arise 

 from them by subdivision, thus rendering possible the pro- 

 duction, in all future generations, of males and females in 

 nearly equal proportions. He also shows that there is a 

 special provision for the production of slight variations in 

 successive generations in a way too complex to be explained 

 here. This, of course, is largely speculation, but it is based 

 at every step on observed facts in the processes of fertilisa- 

 tion and cell-division. 1 



1 The reader will see that the diagrams referred to in Weismann's statements, 

 quoted above, do not seem to represent accurately what he says. They must, 

 therefore, be taken as "diagrams" only, not detailed "figures" of what is seen, 

 which are often so complex that it is difficult to follow the essential details. 

 They are for the purpose of indicating definite stages in the process of the 



