38 HEREDITY AND SELECTION IN SOCIOLOGY 



of the Protozoa, the number of the determinants will probably 

 be considerable ; for, although we are unable, with our present 

 means of observation, to detect the autonomous variation of 

 the cell organs in the Protozoa, we must conclude that the In- 

 fusorians, for instance, possess variable cell organs. In the case 

 of the higher Metazoa, including man, the number of determi- 

 nants must be very large ; for in the organism of the higher 

 animals everything is specialised, and can only be changed by 

 means of autonomous variation in the germinal substance. 

 There are many cases, however, of structures of identical nature 

 — for instance, the hair on the bodies of mammals, or the scales on 

 the wing of the butterfly — of which it cannot be said that every 

 hair or every scale is capable of independent variation. On the 

 contrary, it is rather certain areas, so to speak, which can vary 

 independently, and then we may say that the hairs or scales 

 of that area are determined in the germ-plasm by a single deter- 

 minant. 



To sum up, the germ-plasm or hereditary substance of all 

 multicellular organisms is composed of a number of chromo- 

 somes or idants (groups of ids), whose number varies according 

 to the species, but is constant for each species. Each id contains 

 the sum total of the features, characteristics, and dispositions 

 of the individual in the shape of a number of determinants, each 

 one of which stands in precise and well-defined relation to some 

 hereditary variable part of the organism. Each kind of deter- 

 minant is contained in the germ-plasm as many times as there 

 are ids in that germ-plasm. Each determinant possesses a well- 

 defined structure, and is composed of a mass of differentiated 

 biophors, or elementary living particles, capable of growth and 

 of reproduction by division. 



