184 THE GERM-PLASM 



I assume that germ-cells can only be formed in those parts of 

 the body in which germ-plasm is present, and that the latter is 

 derived directly, without undergoing any change, from that 

 which existed in the parental germ-cell. Hence, according to 

 my view, a portion of the germ-plasm contained in the nucleus 

 of the egg-cell must remain unchanged during each ontogenv, 

 and be supplied, as such, to certain series of cells in the develop- 

 ing body. This germ-plasm is in an inactive condition, so that 

 it does not prevent the active idioplasm of each cell from im- 

 pressing a specific character on the latter in a greater or less 

 degree. It must, moreover, differ from ordinarv idioplasm, 

 inasmuch as the determinants it contains are kept closely to- 

 gether, and are not distributed in groups among the daughter- 

 cells. This accessory germ-plasm is thus passed on in an 

 unalterable condition through longer or shorter series of cells, 

 until it ceases to be inactive in a certain group of cells, more or 

 less remote from the egg-cell, and then impresses upon the par- 

 ticular cell the character of a germ-cell. The transmission of 

 tlie germ-plasm from the ovum to the place of origin of the re- 

 productive cells (• Keimstatte ") takes place in a regular manner, 

 through perfectly definite series of cells which I ci}A.gervi-tracks. 

 These are not actually recognisable, but if the pedigree of the 

 cells in the embryogeny is known, they may be traced from their 

 termination in the germ-cells backwards to the ovum. 



This assumption is supported by the fact that a direct, or at 

 any rate a very close, connection can be proved to exist, although 

 only in rare instances, between the germ-cells of two consecu- 

 tive generations. In the Diptera the first division of the egg- 

 cell separates the nuclear material of the subsequent germ-cells 

 of the embrvo from that of the somatic-cells, so that in this 

 case a direct continuity can be traced between the germ-plasm 

 in the germ-cells of the parent and offspring. 



The process in this case must certainly, however, be looked 

 upon, not as a primary one which has been passed on unchanged 

 from very ancient times, but as a special arrangement peculiar 

 to this order of insects. It nevertheless proves the possibility 

 of each generation of germ-cells being derived directly from the 

 preceding one. and also that the germ-plasm which has been 

 prevented from taking part in the construction of the somatic 

 portion of the embryo is not required in this process. 



We may next take the case of the embryogeny of the 



