One of the imaginary granules or atoms which, according to
   Darwin's hypothesis of pangenesis, are continually being thrown off
   from every cell or unit, and circulate freely throughout the system,
   and when supplied with proper nutriment multiply by self-division and
   ultimately develop into cells like those from which they were derived.
   They are supposed to be transmitted from the parent to the offspring,
   but are often transmitted in a dormant state during many generations
   and are then developed. See Pangenesis.