ever pure but hybrid. Every female with notch wings bred
to a wild male, will produce in equal numbers notch winged daughters and
daughters with normal wings. There will be half as many sons as daughters.
The explanation of this peculiar result is quite simple. Every notch winged
female has one X chromosome that carries the factor for notch and one X
chromosome that is "normal". Daughters receiving the former chromosomes are
notched because the factor for notch is dominant, but they are not killed
since the lethal effect of the notch factor is recessive to the normal
allelomorph carried by the other chromosome that the daughters get from
their father. This normal factor is recessive for notch but dominant for
life. This same figure (b) is used here to show three other sex linked
characters. The spines on the thorax are twisted or kinky, which is due to
a factor called "forked". The effect is best seen on the thorax, but all
spines on the body are similarly modified; even the minute hairs are also
affected. Ruby eye color might be here represented--if the eyes in the
figure were colored. The lighter color of the body and antennae is intended
to indicate that the character tan is also present. The light color of the
antennae is the most certain way of identifying tan. The tan flies are
interesting because they have lost the positive heliotropism that is so
marked a feature in the behavior of D. ampelophila. As this peculiarity of
the tan flies is inherited like all the other sex linked characters, it
follows that when a tan female is bred to a wild male all the sons inherit
the recessive tan color and indifference to light, while the daughters show
the dominant sex linked character of their father, i.e., they are "gray",
and go to the light. Hence when such a brood is disturbed the females fly
to the light, but the males remain behind.

One of the first mutants that appeared in D. ampelophila was called
rudimentary on account of the condition of the wings (c). The same mutation
has appeared independently several times. In the drawing (c) the dark body
color is intended to indicate "sable" and the lighter color of the eyes is
intended to indicate eosin. This eye color, which is an allelomorph of
white, is also interesting because in the female the color is deeper than
in the male. In other cases of sex linked factors the character is the same
in the two sexes.

In the fourth figure (d) the third and fourth longitudinal vein