16 HEREDITY AND SELECTION IN SOCIOLOGY 



formation of the two daughter nuclei ; and, indeed, these daughter 

 nuclei do not take long in defining themselves, each group of 

 chromosomes forming an enveloping membrane, and the chro- 

 matin substance distributing itself, as in the original nucleus, 

 in a sort of network throughout the new nucleus (G). 



Such is the process of cell division, as efEective as it is wonder- 

 ful. Its result is clear. By means of the karyoMnesis the chro- 

 matin substance is divided into two perfectly equal halves, which 

 go to form the nuclei of the two daughter cells. This fact alone, 

 the extraordinary precision of the mechanism by which this 

 equal division is effected, sufficiently proves the essential im- 

 portance of the chromatin substance. As a result of the karyo- 

 kinesis, half of the hereditary substance is transmitted to the 

 one, half to the other daughter cell. The constant number of 

 chromosomes which is maintained throughout all the cells of the 

 body, the reduction of that number by half as a result of the 

 so-called reducing divisions during the maturation of the germ- 

 cells, justify the beUef that the chromosomes are distinct physio- 

 logical and morphological individualities. But the indispensable 

 character of the chromosomes has been finally placed beyond 

 doubt by microscopic vivisection experiments practised on 

 unicellular organisms. These experiments have shown that 

 Infusorians which are artificially halved are capable of repro- 

 ducing the whole organism from either half, -provided that the half 

 in question contains a 'piece of the nudeus, and not othericise. 

 Thus it is certain that it is the nucleus which contains the matter 

 capable of continuing the Hfe of the cell, and, through the life of 

 the cell, the life of the developed organism. 



In the case of nearly all multicellular organisms reproduction 

 is effected by means of a special germinal substance. The new 

 individual is developed from a particular substance contained in 

 particular cells — the reproductive or germ cells. This substance, 

 which transmits from one generation to another those properties 

 which combine to give the offspring the form and organisation 



