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 larvae of Hawaiian Droso- 

 philinse. I am inclined to think, however, that these fonns are not 

 very serious enemies. They do not often emerge from exposed fruit 

 that contains Drosophila larvae and pupae. 



Predacious enemies: Fermenting fruit frequently contains predacious 

 beetle larvae (Staphylinidae and apparently Nitidulidae), that must 

 destroy many Drosophila larvae. I think these are probably the most 

 serious natural enemies of Drosophilinse. 



I have seen domestic fowls scratching apart fleshy fungi and eating 

 the larvae contained therein. These larvae were chiefly Phoridae, but 

 some of them were Drosophilinae {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 fiavida Williston, destroy many Drosophilinae 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 

 laeen made sufficiently 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 larvae 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 Drosophilinae are shown in plate 1. 

 Those of Drosophila melanogaster are about 0.6 mm. long, those of 

 Chymomyza procnemis about 0.5 nam. 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 follicle cells that secreted the chitinous 

 egg-shell. The filaments at the anterior end are present in all the 



