Ndgcli's Idioplasm 57 



that case the germ-plasm must evidently consist, every- 

 where, of these same components, and, in the lowest 

 organisms, in which fertilization does not take place, as 

 well as in the germ-cells of the higher plants and animals, 

 we must assume, as the material basis of heredity, numer- 

 ous material bearers, which correspond to the individual 

 hereditary characters, and are not inseparably united. This 

 assumption, however, makes that of the ancestral plasms 

 completely superfluous. Thus it is easily seen that the 

 whole ancillary hypothesis regarding an occasional nu- 

 merical reduction of the ancestral plasms may fail. 



In a word : In a consideration of the differentiation 

 of organs, Weismann's theory of itself leads to the quite 

 opposite assumption of individual material bearers for 

 the individual hereditary characters. 



7. NdgclTs Idioplasm 



In his niechanico-physiological theory of descent, 

 Nageli, a few years ago, advanced the concept of the 

 idioplasm^'"^ In distinction to the other protoplasms, it 

 is the bearer of the hereditary qualities. A factor (an- 

 lage) representing every perceptible character, is present 

 in it; in every individual of the same species, even in 

 every organ of a plant, it has a slightly different compo- 

 sition. It is not limited to the nucleus, but runs through 

 the entire protoplast as a strand with many windings. All 

 cross-sections of this strand are alike, each one containing 

 every hereditary tendency. That is why, in cell-division, 

 the daughter-cells, with their part of the strand, are also 

 endowed with all the hereditary factors. 



The nature of the idioplasm is determined by its mole- 



^^Nageli, C. von. Mechanisch-physiologische Thcoric dcr Ah- 

 stammungslehrc. pp. 21-31. 1884. 



