The Embryo at the Wound 43
one species contained the same number of chromosomes. As growth pro-
ceeded by mitosis, these chromosomes split lengthwise to make two of
each so that each daughter cell then had the same number of chro-
mosomes. The egg and sperm, dividing by a special process called
meiosis, wound up with exactly half that number, so that the fertilized
egg would start out with a full complement, half from the father and
half from the mother. He reached the obvious conclusions that the chro-
mosomes transmitted heredity, and that each one could exchange smaller
units of itself with its counterpart from the other parent.
MEIOSIS—FORMATION OF SEX CELLS