The male passes three days in the egg, six and a half as a worm, and metamorphoses into a fly on the twenty-fourth or twenty-fifth day, after the egg is laid. The great epoch of laying the eggs of males may be accelerated or retarded by the state of the atmosphere promoting or impeding the collections of the bees. The _development_ of _each_ species likewise proceeds more slowly when the colonies are weak or the air cool, and when the weather is very cold it is entirely suspended. Mr. Hunter has observed that the eggs, maggots and nymphs, all require a heat above 70° of Fahrenheit for their evolution. The influence of temperature in developing embryo insects is very strongly illustrated in the case of the _Papilio Machaon_. According to Messrs. Kirby and Spence, "if the caterpillar of the _Papilio Machaon_ becomes a pupa in July, the butterfly will appear in thirteen days; if it do not become a pupa till September, the butterfly will not make its appearance until the following June." And this is the case, say they, with a vast number of other insects. Reaumur proved the influence of temperature, by effecting the regular changes in a hot-house, during the month of January. He also proved it conversely, by having recourse to an ice-house in summer, which enabled him to retard the development for a whole year. "The larvæ of bees, though without feet, are not always without motion. They advance from their first station at the bottom of the cell, in a spiral direction: this movement, for the first three days, is so slow as to be scarcely perceptible; but after that it is more easily discerned. The animal now makes two entire revolutions, in about an hour and three quarters; and when the period of its metamorphosis arrives, it is scarcely more than two lines from the mouth of the cell. Its attitude, which is always the same, is a strong curve. This occasions the inhabitant of a horizontal cell to be always perpendicular to the horizon, and that of a vertical one to be parallel with it[F]." [Footnote F: Kirby and Spence.]