REPR OD UCTION. 503 



origin of sex — germ-plasm is continuous from individual to individual along 

 any one line of descent. Weisniaun draws a sharp line between germ-plasm, 

 and somatoplasm, or body-plasm, which latter comprises all protoplasm that 

 the body contains except the germ-plasm. Germ-plasm once originated con- 

 tinues from generation to generation ; somatoplasm develops anew in each gen- 

 eration from germ-plasm by growth and differentiation, resulting in a loss of its 

 specific germinal character. Germ-plasm is stable in composition ; somatoplasm 

 is variable. Germ-plasm, being passed on from parent to offspring, is immortal ; 

 somatoplasm dies when the individual dies. Weismann believes that "the 

 germ-plasm possesses a fixed architecture, which has been transmitted histori- 

 cally " and which represents the parts of the future organism. It consists of 

 material particles or hereditary units called determinants, each of which has a 

 definite localized position within the germ-plasm. The determinants are sug- 

 gestive of Darwin's gemmules, yet they are not the same, for, while gemmnles 

 were supposed to represent individual cells, determinants are representatives 

 of cells or groups of cells that are variable from the germ onward. Deter- 

 minants consist of definite combinations of simpler units, or biophors, which 

 are the smallest particles that can exhibit vital phenomena. Below biophors 

 there come in order of simplicity of material structure the molecules and 

 the atoms of the physicist. Above biophors and determinants Weismann 

 finds it necessary to assume the existence of higher units, named in order ids 

 and idants, the former being groups of determinants, and actually visible as 

 granules of chromatin, the latter being the chromosomes of the nucleus. Each 

 one of these various units is possessed of the fundamental vital properties of 

 growth and multiplication by division. Such a complex system is Preforma- 

 tion in an extreme form. In fertilization idants of the sperm join with idants 

 of the ovum, and the resulting segmentation nucleus consists of a mixture of 

 paternal and maternal determinants. Within this mixture there exist in a 

 potential state the primary constituents of a considerable number of forms 

 which the future individual may assume. In ontogeny, or development of 

 the individual, these primary constituents take two paths: some of the ids 

 remain inactive and enter the germ-cells of the embryo for the production of 

 future generations ; other ids disintegrate into determinants, the determinants 

 enter the embryonic cells that result from segmentation, and there themselves 

 disintegrate and set free into the cytoplasm their constituent biophors; thus 



they determine the future character of the cells of th 'ganisrn. The division 



of primary constituents into those that shall remain latent and those that shall 

 become active is effected largely by the stimulation of external influences; 

 hence, given several potential formations in the germ, external influences 

 decide which one shall become the actual structure in the adult organism. 

 Once set free and having become somatoplasm, neither the biophors nor the 

 determinants are able to return to the germ-cells. In the adult, germ-plasm is 

 never capable of reflecting in any way the characteristics of the somatoplasm 

 which surrounds it on all sides. With its ancient ancestry it leads a charmed 

 existence, largely independent of environmental changes. It follows that 



