It is therefore most desirable to pull up and burn the infested plants as soon as possible. A proper rotation of crops should also be practised. [The =Onion Fly= (_A. ceparum_) maggot feeds within the bulbs of stored onions. The male fly is grey, the female yellow.] [Illustration: FIG. 116.—A turnip infested by the Cabbage Fly: A, swellings; G, tunnels. ] The =Cheese Fly= (_Piophila casei_), one-fifth of an inch long, slender, with a metallic sheen, almost hairless, black, with dirty yellow legs and wings of glassy clearness. These small flies abound in front of the windows of places where cheese is stored; in summer and autumn the shining white maggots, which are cylindrical in form with tapering ends, and one-third of an inch long, live in large numbers in old cheese, gnawing it through and through, and making it dirty. Now and then they spring forwards by bending their bodies into a circle and suddenly straightening them again. They become pupæ on the walls or in straw, near the cheeses from which they have crept out. _Remedies_: Keeping the cheeses clean; mechanical exclusion (gauze screens outside the windows, enclosure in chests). The =Green-eyed Flies= (_Chlorops_) include a number of small flies, under one-sixth of an inch long, with spherical head, rounded greenish eyes, strongly arched thorax, and short egg-shaped abdomen, pointed in the male and blunt in the female. The headless larvæ live in the haulms of grasses and species of grain; the life history of a few forms only is adequately known. A few are harmful, especially as there are two or three generations annually. The late summer generation often appears in large numbers, indeed in actual swarms. Since no species lives exclusively on corn, it is impossible to keep them down for a long period of time. I describe only two species:— [Illustration: FIG. 117.—The Ribbon-footed Corn Fly (_Chlorops tæniopus_). ]