Pangenesis was Charles Darwin's mechanism for heredity. He presented this 'provisional hypothesis' in his 1868 work The Variation of Animals and Plants Under Domestication and felt that it brought 'together a multitude of facts which are at present left disconnected by any efficient cause'. The theory itself was deeply flawed and just plain wrong, yet it represents Darwin's attempt to explain such diverse phenomona as atavisms, the intermediate nature of hybrids (blending inheritance), Lamarckian use and disuse, and limb regeneration.
Simply put, the theory holds that body cells shed 'gemmules' which collect in the reproductive organs prior to fertilization. Thus every cell in the body has a 'vote' in the constitution of the offspring. Atavisms arise due to the awaking of long-dormant gemmules while limbs regenerate due to the activation of gemmules from the missing limb which circulate in the main part of the body.