ticles
that give the blue color. In addition, in many eyes much brown pigment
is formed which may be small in amount and gathered around the pupil or
so extensive as to suffuse the entire iris and make it all brown. It is
seen, then, that the brown iris is formed by something additional to the
blue. And brown iris may be spoken of as a _positive_ character,
depending on a determiner for brown pigment; and blue as a _negative_
character, depending on the absence of the determiner for brown.

Now when both parents have brown eyes and come from an ancestry with
brown eyes, it is probable that all of their germ cells contain the
determiner for brown iris pigmentation. So when these germ cells, both
carrying the determiner, unite, all of the progeny will receive the
determiner from both sides of the house; consequently the determiners
are double in their bodies and the resulting iris pigmentation may be
said to be _duplex_. When a character is duplex in an individual, that
means that when the germ cells ripen in the body of that individual
each contains a determiner. So that individual is capable, so far as he
is concerned, of transmitting his trait in undiminished intensity.

If a parent has pure blue eyes, that is evidence that in neither of the
united germ cells from which he arose was there a determiner for iris
pigmentation; consequently in respect to brown iris pigmentation such a
person may be said to be _nulliplex_. If, now, such a person marry an
individual duplex in eye color, in whom all of the germ cells contain
the determiner, each child will receive the determiner for iris
pigmentation from one side of the house only. This determiner will, of
course, induce pigmentation, but the pigmentation is simplex, being
induced by one determiner only. Consequently, the pigmentation is apt to
be weak. When a person whose pigment determiners have come from one side
of the house forms germ cells, half will have and half will lack the
determiner. If such a person marry a consort all of whose germ cells
contain the determiner for iris pigmentation, all of the children will,
of course, receive the iris pigmentation, but in half it will be duplex
and in the other half it will be simplex. If the two parents both be
simplex, so that, in each, half of the germ cells possess and half lack
the determiner in the union of germ cells, there are four events that
are equally apt to occur: (1) an egg _with_ the determiner unites with a
sp