NAGELI'S IDIOPLASM 9 



has been applied to the emboitement theory and to the 

 pangenesis theory, can also be applied here. 



A theory of quite a different kind is Nageli's " idioplasm 

 theory." ] It assumes the existence of a particular substance 

 the idioplasm and it is through this substance -that the 

 hereditary characters are transmitted from parent to off- 

 spring. The idioplasm is of course different in every different 

 kind of animal and plant, and it is to this intrinsic differ- 

 ence in substances that the different characters of different 

 organisms are due ; it is, in fact, supposed to regulate the 

 process of development, and the lines along which develop- 

 ment will go. The idioplasm itself is supposed to alter in its 

 organisation, and this alteration is supposed to precede the 

 differentiation which occurs among the cells that go to form 

 the body of the multicellular organism. This theory has 

 been developed along different lines, and in some cases by 

 advocates of the hypothesis of pangenesis and of the 

 localisation theory. Thus Weismann and Roux believed 

 that the idioplasm was not a particular compound with 

 particular properties and characters, but was a complicated 

 mixture of many different substances, each particular sub- 

 stance representing a particular character. 2 Here we again 

 see the embottement theory looming up. Instead of holding 

 that all the characters developed in a multicellular indi- 

 vidual were due to the presence of one particular kind of 

 substance in all the cells of the organism, this development 

 of the idioplasm theory necessitates the assumption of in- 

 numerable different kinds of substance, which, as succeeding 

 generations of cells are produced from the fertilised ovum 

 in the building up of the various tissues, are divided in a 

 qualitative manner, each group of cells in the later cell 

 generations receiving portions of the idioplasm which was 

 present in the ovum, different from those portions received 



1 Nageli, C., Mechanisch-physiologisclie TJworie der Abstammungslehre, 

 Miinchen und Leipzig, 1884. 



2 Weismann, A., The Germ Plasm, New York, 1893 ; Roux, W., Uber die 

 Betendung der Kernteilungsfiguren, Leipzig, 1883. 



