In 1890, W. Heape published an account of some experiments with rabbits. Taking the fertilized egg of an angora rabbit (i. e., a long-haired, white one) from the oviduct of its mother previous to its attachment to the wall of the uterus, he transferred it to the uterus of a Belgian hare, a rabbit which is short-haired and gray. The egg developed normally in the new body and produced an animal with all the characteristics, as far as could be seen, of the real mother, rather than the foster-mother. Its coat was long and white, and there was not the slightest trace of influence of the short, gray-haired doe in whose body it had grown.

Here was a case in which environment certainly failed to show any modifying influence. But it was objected that the transplanted egg was already full-grown and fertilized when the transfer was made, and that therefore no modification need be expected. If the egg were transferred at an earlier stage, it was thought, the result might be different.

W. E. Castle and J. C. Phillips therefore undertook an experiment to which this objection should not be possible.[195]

"A female albino guinea-pig just attaining sexual maturity was by an operation deprived of its ovaries, and instead of the removed ovaries there were introduced into her body the ovaries of a young black female guinea-pig, not yet sexually mature, aged about three weeks. The grafted animal was now mated with a male albino guinea-pig. From numerous experiments with albino guinea-pigs it may be stated emphatically that normal albinos mated together, without exception, produce only albino young, and the presumption is strong, therefore, that had this female not been operated on she would have done the same. She produced, however, by the albino male three litters of young, which together consisted of six individuals, all black. The first litter of young was produced about six months after the operation, the last about one year. The transplanted ovarian tissue must have remained in its new environment therefore from four to ten months before the eggs attained full growth and were discharged; ample time, it would seem, for the influence of a foreign body upon the inheritance to show itself were such influence possible."

While such experiments must not be stretched too far, in application to the human species, they certainly offer striking evidence of the fact that the characters of any individual are mainly due to something in the germ-plasm, and that this germ-plasm is to a surprising degree independent of any outside influence, even such an intimate influence as that of the body of the mother in which it reaches maturity.