irs of large chromosomes, and
one small group of characters and one pair of small chromosomes.

THE FOUR GREAT LINKAGE GROUPS OF DROSOPHILA AMPELOPHILA

The following description of the characters of the wild fly may be useful
in connection with the account of the modifications of these characters
that appear in the mutants.

The head and thorax of the wild fly are grayish-yellow, the abdomen is
banded with alternate stripes of yellow and black. In the male, (fig. 4 to
right), there are three narrow bands and a black tip. In the female there
are five black bands (fig. 4 to left). The wings are gray with a surface
texture of such a kind that at certain angles they are iridescent. The eyes
are a deep, solid, brick-red. The minute hairs that cover the body have a
very definite arrangement that is most obvious on the head and thorax.
There is a definite number of larger hairs called bristles or chaetae which
have a characteristic position and are used for diagnostic purposes in
classifying the species. On the foreleg of the male there is a comb-like
organ formed by a row of bristles; it is absent in the female. The comb is
a secondary sexual character, and it is, so far as known, functionless.

Some of the characters of the mutant types are shown in figures 53, 54, 55,
56. The drawing of a single fly is often used here to illustrate more than
one character. This is done to economize space, but of course there would
be no difficulty in actually bringing together in the same individual any
two or more characters belonging to the same group (or to different
groups). Without colored figures it is not possible to show many of the
most striking differences of these mutant races; at most dark and light
coloring can be indicated by the shading of the body, wings, or eyes.

_Group I_

In the six flies drawn in figure 53 there are shown five different wing
characters. The first of these types (a) is called cut, because the ends of
the wings look as though they had been cut to a point. The antennae are
displaced downward and appressed and their bristle-like aristae are
crumpled.

[Illustration: FIG. 53. Group I. (See text)]

The second figure (b) represents a fly with a notch in the ends of the
wings. This character is dominant, but the same factor that produces the
notch in the wings is also a recessive lethal factor; because of this
latter effect of the character no males of this race exist, and the females
of the race are n