To estimate the whole population, I pack it into a glass tube eighteen millimetres [67] in diameter. The column thus formed occupies a height of 56 millimetres. [68] The volume, therefore, amounts to 16,532 cubic millimetres. [69] Therefore, allowing one Louse, roughly, to each cubic millimetre, the population of the gall is about sixteen thousand. As I cannot count, I gauge. Even so did Herschel [70] gauge the Milky Way. For numerical infinity, the Louse vies with the star. In four months the black atom, the first pioneer of the gall, has left all these descendants; and the end is not yet. CHAPTER IV THE TEREBINTH-LOUSE: THE MIGRATION By the end of September the horn-shaped gall is full, almost as full as a keg of anchovies. There would not be room for them all were the Lice to form only one layer, side by side, with their suckers implanted. They lie in strata according to the length of their probe: uppermost are the big Lice, in the second layer the medium-sized and between their legs the small ones, all of them motionless, with their trunks at work. Above those engaged in drinking is the shifting horde, seeking a place at the refreshment bar. Eddies occur in the crowd: those at the top dive down, those underneath return to the surface; and this continual ebb and flow gives each one time for a little tippling. In this rough and tumble the white waxen finery turns to flour, which fills up the interstices and makes of the whole a swarming conglomerate in which the metamorphosis is effected. Here, without a moment’s quiet, the moult takes place and not a leg is out of joint: here, when there is no free space, wide wings are unfurled and not a wing is torn. To achieve transfiguration without a hitch in such a tumult the insect must be peculiarly favoured by fortune. The pot-bellied orange Lice are now handsome, black, slender midges, provided with four wings. Their secluded life is over; the time has come for soaring in the open air. But how will they get out? The internees are quite incapable of making a breach in the ramparts: they have no tools. Well, what the prisoners cannot accomplish the fortress itself will do. When the population is ripe the gall is ripe too, so closely does the calendar of the bush synchronize with that of the insect. The hems raise their upper folds a little; the spindles open like so many purses, each lined with pink satin; the auricles part their thick gnarled lips. The doors open of themselves for the impatient inmates, by the mere action of the sap. In the other galls, the globular and horn-shaped ones, the mechanism does not work so easily; the unclosing is a violent affair. More and more distended day by day, the globes burst their sides in star-shaped rents, while the horns split open at the top.