is usually attained in less than two weeks; they then pass two more weeks in the pupal stage, when the perfect insect appears. When dogs are badly infested by them, the use of common olive-oil is recommended. This should be well rubbed into the hair and over the skin, being allowed to remain for half an hour, when it should be washed out with the best yellow soap and lukewarm water. Dalmatian insect-powder has also been found efficacious. This powder can be rubbed into the hair, and it can be sprinkled around their kennels. It is not, however, best to use 
Fig . 6.—Larva of Flea. it on cats, but possibly it might do no harm to sprinkle it around their sleeping-places. A better plan is to have the cat's bed made of shavings or some such material that can often be replaced, the old bedding being carefully taken up and burned.
Some years ago there were on exhibition a number of so-called educated fleas, and it is thought by some people that the intelligence of fleas must be very great if they can be trained in this way; but an article by Mr. W. H. Dall, in the American Naturalist, a few years ago, showed that in every case the motions made by the flea were caused, not by the training it had received, but by the struggles made in its efforts to escape.
House-Fly (Musca domestica).—Familiar as we all are with this insect in its mature state, it will be found that to many its history before it appears in our houses is still very obscure, and until some years ago, when Dr. Packard made a study of its life-history, naturalists, too, were somewhat unfamiliar with its early stages of growth, and to him we are indebted for the following facts:
We find the flies most annoying and abundant in the hot dog-days of August, and, unless the greatest care is taken, our rooms are filled with them, even though we maybe some distance from a stable, where the desired food for the young is found. The eggs are laid in bunches in manure, often buried out of sight, and, the conditions being favorable, they are hatched in twenty-four hours. The worm or maggot has no legs, and, after changing its skin, appears larger, though otherwise remains about the same in appearance. After two or three days it again sheds its skin, and in this stage of development it remains two or three days longer. It then transforms into a chrysalis, in which state the body contracts somewhat and becomes brown and hard, and, after six or seven days, the perfect fly appears and lives for five or six weeks, perhaps longer. A few flies probably live over the winter in crevices of buildings until the warm spring days bring them out.
