30 HEREDITY AND SELECTION IN SOCIOLOGY 



transmission to each cell, or each group of cells, of those pro- 

 perties by means of which the appropriate organisation, struc- 

 ture, and composition are effected. Its function is, consequently, 

 the deiermining of the soma. We have seen how the germ-plasm 

 is organised in order to fulfil this function. Biophors, deter- 

 minants, ids, are arranged within it in complex architecture, 

 different for each species. How, then, does the germ-plasm 

 determine the somatic cells ? 



The reply is : Through the distribution of the ids in the process 

 of development. The ids contained in the cell nucleus break 

 up into groups of component determinants, into dissimilar 

 groups produced by unequal division of the ids. We shall see 

 the reason for this unequal division shortly. The determinants 

 in turn break up into their component biophors ; the biophors 

 are distributed to the various cells, and determine the function 

 and form of these cells. 



Each determinant, or group of determinants, stands in definite 

 relation to definite cells or groups of cells in the fully formed 

 organism ; that is to say, a given part of the animal is deter- 

 mined, both as regards its existence and as regards its nature, 

 by a corresponding part of the germ-plasm — i.e., by a corre- 

 sponding determinant or group of determinants. Thus the cells 

 of an organ X are determined by the determinant X^, alike in 

 their existence and in their nature ; the cells of an organ Y by 

 the determinant Y^, etc. That part of the organism which is 

 determined by a given determinant is known as the " deter- 

 minate." 



The determinants of two corresponding organs in the same 

 individual, or the determinants of the same organ in two 

 different individuals, are homologous with one another. Thus 

 the determinants of the right hand are homologous with the 

 determinants of the left, and the determinants which in one 

 parent correspond to a given determinate X are homologous 

 with those determinants which in the other parent correspond 



