204 THE GERM-PLASM 



In order to give a satisfactory answer to these questions, I 

 have assumed the existence of a germ-plasm, but have not 

 primarily regarded this as a 'special reproductive substance'^ 

 which is very dijTerent from all other substances in the body ; 

 I have looked upon it, on the contrary, as the substance which 

 gives rise to all the other formative substances of the entire 

 individual. Every part of the body contains a portion of this 

 substance, and the whole organism can only be formed anew 

 when all the portions of this controlling substance (the idio- 

 plasm) are combined ; that is to say, when germ-plasm is 

 present. The assumption of germ-idioplasm or germ-plasm 

 is, I consider, quite unavoidable, for we must at the present 

 day take it as proved that the hereditary tendencies are con- 

 nected with a substance. In my opinion, it is also an irrefutable 

 fact that this germ-plasm undergoes regular changes from the 

 ovum onwards : it must, indeed, undergo change from cell to 

 cell, for we know that the individual cell is the seat of the forces 

 which give rise collectively to the functions of the whole. The 

 forces which are virtually contained in the germ-plasm can 

 therefore only become apparent when its substance undergoes 

 disintegration, and its component parts, the determinants, be- 

 come rearranged. The difference in function seen in the various 

 groups of cells in the body compels us to suppose that these 

 contain a substance which acts in various ways. The cells are 

 therefore centres of force of differ oit worth, and the substance 

 {idioplasm) which controls them must be Just as dissimilar as 

 are the forces developed by them. 



The apparent similarity of many young plant-cells may account 

 for the vagueness with which Vines, following Sachs's example, 

 speaks of an 'embryonic substance' irom. which reproduction is sup- 

 posed to proceed in all cases, and which is assumed to be present 

 in all 'young ' cells. In my opinion the hereditary value of a cell 

 can be estimated as little by its age as by its appearance. The 

 mass of cells resulting from the segmentation of an animal egg 

 certainly possess the character of youth, and in a certain stage of 

 development these cells are all of the same age and all look 

 alike. They have, however, entirely different hereditary values ; 

 and if we are accurately acquainted with the ontogeny of the 

 animal in question, we can tell what hereditary tendencies lie 

 hidden in each cell. The primary constituents of the entire endo- 

 derm, for instance, mav be contained in one cell, and that of the 



