Weismann’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.” 41° 
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- 
119Qscar Hertwig: Die Zelle und die Gewebe. II. P. 180. 
