340 PROCEEDINGS OF THE 



unmasked by science as one of man's greatest enemies. It lias 

 110 true teeth, but obtains its food by suction. This passes into 

 the crop and subsequently overflows into the true stomach. 

 When the fly alights on any solid substance, such as sugar or 

 I'old meat, it vomits the contents of its crop upon it to soften 

 the material, which it contaminates to our cost. House flies 

 will vomit fifteen times an hour and defecate ten times ; these 

 habits constitute their supreme danger to mankind. The aver- 

 age of many fly censuses taken in England and America gives 

 the different species of house flies the following percentage : 

 Common house fly, 82 per cent. ; lesser house fly, 14 per 

 cent. ; stable fly, 1 per cent. ; blow fly, 1 per cent. ; other 

 species, 2 per cent. The wings move with great velocity : 

 in flying they make 330 complete strokes in a second. Nearly 

 the entire thorax is filled with the muscles connected with the 

 Avings, but the tracheal or respiratory system occupies more 

 space than any other; this makes the creature very buoyant. 

 Under the back of the wings are two drumstick-shaped append- 

 ages known as halteres, which are very characteristic of the 

 Diptera. Their purpose is not certainly known, but they 

 are supplied with, next to the optic nerve, the largest nerve 

 in the body. The mechanism of the proboscis was explained; 

 the long salivary glands and the intestinal system described. 

 The eyes, with their 4,000 lenses, and the three ocelli on 

 the top of the head referred to. Each of the ovaries contains 

 about 75 eggs in various stages of development ; 150 are laid 

 from four to six times in the life of the fly, but the blow fly lays 

 1,000 each time. The immense number of flies that one pair 

 would produce in a season, if all the progeny survived, was men- 

 tioned, one authority putting it at 500,000,000. The time taken 

 by the fly in passing through its life circle was spoken of ; it 

 depends greatly upon the temperature and general conditions, 

 but in the summer may be accomplished in about ten days. Its 

 ordinary life lasts about seven weeks. " Fortunately, flies have 

 their enemies : thread worms discomfort them from within, and 

 the fungus Empusa muscae attacks them from without with 

 deadly ellect. Mites worry them, beetles devour their larvae, 

 and wasps, robber flies, spiders, centipedes, ants, lizards and 

 birds all take their toll. One of the most unfortunate parts of 

 their anatomy is the innumerable hairs with which their bodies 



