METHODS OF COLLECTING AND PRESERVING DROSOPHILINE.   45

D. simulans, D. funebris, D. obscura, D. affinis, and D. cardini this
difference is quite well marked.

Size: In most species the males average a little smaller than the
females. In the case of D. melanogaster this size difference is a true
secondary sexual character, as has been shown by an examination of a
large series of gynandromorphs (Morgan and Bridges, 1919). In these
specimens male and female parts are combined in the same individual;
and it is regularly observed that the male parts are a trifle smaller and
bear somewhat smaller bristles and hairs. I have observed the same
relation in gynandromorphs of D. simulans.

Abdominal structure: As has been pointed out above, the abdominal
structure of the two sexes is different in the genus Drosophila. The
female has seven well-developed dorso-lateral plates, the male only
five. The spiracles are correspondingly different—the female has
one on the fifth segment and one on the sixth, while the male has two
on the fifth. The ventral abdominal plates are also different. The
female has six, the male four, and the posterior members of the series
are quite different in shape in the two cases.
 

IX. METHODS OF COLLECTING AND PRESERVING
DROSOPHILINAE.

Most of the Drosophilinse feed on fruit or on fungi, or have leaf-
mining larvse. The most efficient places to collect them are where food
is plentiful. Fruit in grocery stores will yield the commoner species,
and more especially the widely distributed ones that are presumably
introduced. Windfall apples or other decaying fruit usually repays
examination. Tomato patches, even before the fruit is ripe, are
worth sweeping. Garbage piles usually have many species. Fleshy
fungi, either agarics or Boletinse, will yield many forms; they are
more prolific after they have decayed somewhat. Bleeding trees should
always be examined.

My own practice has been to expose fruit in the woods, and collect
from it daily for a while. The fruit is usually placed in a bottle and
hung in a low tree. This method makes it less likely to be stolen by
small mammals, and makes collecting easy, as one simply pours the
flies into his collecting bottle. After a week or so the bottle may be
brought in, and the larvse and pupse allowed to develop, thus increasing
the collection. For this kind of collecting it is advisable to use many
different sorts of fruit. I have found banana, pineapple, tomato, and
peach to be specially satisfactory.

I always bring the collections into the laboratory alive, in order to
be able to breed any forms that seem desirable. If this is to be done
it is necessary to be careful, especially in the case of sweepings, not
to leave predacious forms (spiders, empidids, asilids, ants, etc.) or large