Weistnann's Accessory Idioplasm 137 



ing tentacles of the snail contain no trace whatever of 

 retinal cells nor of pigment cells, nor of any other sensory 

 cells whatever. Similarly the buds for the extremities do 

 not contain any trace of the material of the carpus and 

 phalanges nor of the muscles and tendons belonging to 

 them. It is a complete new formation." no 



The explanation which Weismann endeavors to give 

 of these complete new formations produced in every re- 

 generation is well known : 



"If each cell of the completely developed bone con- 

 tains within it only that kind of idioplasm which con- 

 trols it and which is consequently the molecular expres- 

 sion of its own particular nature, it would be impossible 

 to understand how the regeneration could be effected of 

 a bone which had been, for instance, cut through lon- 

 gitudinally. Supposing that because of the wound there 

 would become exercised upon the cells of the stump a 

 stimulus which caused them to proliferate, a mass of bony 

 tissue would indeed be produced but never a bone of def- 

 inite size and shape. This can take place only in case the 

 cells undergoing proliferation possess, besides their ac- 

 tive determinants, an additional supply of determinants 

 which control the missing part about to be reformed. It 

 is then evident that, if we wish to transport the Nisus 

 formativus of Blumenbach into the cell and indeed into 

 its idioplasm, we must assume that each cell capable of 

 regeneration contains besides its principal idioplasm, also 

 an accessory idioplasm ('Neben-Idioplasm'), consisting 

 of the determinants of the portion of the amputated organ 

 which can be regenerated by it. Thus, for instance, the 

 cells of the humerus must contain besides their own con- 



110 Oscar Hertwig : Die Zelle und die Gewebe. II. P. 180. 



