18            THE  NORTH  AMERICAN  SPECIES  OF  DROSOPHILA.

Hymenopterous parasites: The young stages of Drosophila are
parasitized by various species of Hymenoptera. Ashmead has de¬
scribed a few species, Martelli (1910) has given an account of others,
and I have bred a few. Perkins (1913) states that he has bred at least
five species of parasitic Hymenoptera (belonging to the proctotrupoid,
cynipoid, and chalcidoid groups) from the larvse of Hawaiian Droso¬
philinse. I am inclined to think, however, that these forms are not
very serious enemies. They do not often emerge from exposed fruit
that contains Drosophila larvse and pupse.

Predacious enemies: Fermenting fruit frequently contains predacious
beetle larvse (Staphylinidse and apparently Nitidulidse), that must
destroy many Drosophila larvse. I think these are probably the most
serious natural enemies of Drosophilinse.

I have seen domestic fowls scratching apart fleshy fungi and eating
the larvse contained therein. These larvse were chiefly Phoridse, but
some of them were Drosophilinse (Leucophenga and Mycodrosophila).

Adults are preyed upon by spiders and by flies of the empidid,
cordylurine, and anthomyiine groups. I have seen an empidid,
Elaphropeza flavida Williston, destroy many Drosophilinse in Cuba,
where the species is common.

Perkins (1913) states that, in Hawaii, a crabronid wasp often fills
its cells with a species of Drosophila.

VI. ANATOMY.

The following account of the structure of the various stages has
been made suflSciently general to apply to all the members of the
genus Drosophila known to me, and usually to the other members of
the subfamily also, unless otherwise stated. In most cases the points
have been worked out first with D. melanogaster, D. funebris, or D.
immigrans, and then checked up by an examination of other species.
Throughout the preparation of this part of the paper I have had on
hand living stocks of about 15 species belonging to the genera Dro¬
sophila, Chymomyza, and Scaptomyza, as well as slides of larvse and
cleared specimens of numerous other forms. Many of the points
have been checked by examination of pinned material of the rarer

species.

EGGS.

The eggs of several species of Drosophilinse are shown in plate 1.
Those of Drosophila melanogaster are about 0.6 mm. long, those of
Chymomyza procnemis about 0.5 mm. All the species in which I have
investigated the matter have white eggs, with a fine meshwork of
raised lines (not shown in the figures) over their surfaces. These are
apparently the remains of the foUicle cells that secreted the chitinous
egg-shell.    The filaments at the anterior end are present in all the