One more step in this direction and the problem of the well is solved. I exhume a larva which happens to be working at its exit-gallery. Very occasionally, I get a piece of luck like this, in the course of my digging; it would be useless for me to try for it, as there is nothing outside to guide my search. My welcome prize is just beginning its excavations. An inch of tunnel, free from any rubbish, and the waiting-room at the bottom represent all the work for the moment. In what condition is the worker? We shall see. The grub is much paler in colour than those which I catch as they emerge. Its big eyes in particular are whitish, cloudy, squinting and apparently of little use for seeing. What good is sight underground? The eyes of the larvæ issuing from the earth are, on the contrary, black and shining and indicate ability to see. When it makes its appearance in the sunshine, the future Cicada has to seek, occasionally at some distance from the exit-hole, the hanging branch on which the metamorphosis will be performed; and here sight will manifestly be useful. This maturity of vision attained during the preparation for the release is enough to show us that the larva, far from hastily improvising its ascending-shaft, works at it for a long time. Moreover, the pale and blind larva is bulkier than it is in the state of maturity. It is swollen with liquid and looks dropsical. If you take it in your fingers, a limpid humour oozes from the hinder part and moistens the whole body. Is this fluid, expelled from the intestines, a urinary product? Is it just the residue of a stomach fed solely on sap? I will not decide the question and will content myself with calling it urine, merely for convenience. Well, this fountain of urine is the key to the mystery. The larva, as it goes on and digs, sprinkles the dusty materials and makes them into paste, which is forthwith applied to the walls by abdominal pressure. The original dryness is succeeded by plasticity. The mud obtained penetrates the interstices of a rough soil; the more liquid part of it trickles in front; the remainder is compressed and packed and occupies the empty spaces in between. Thus is an unblocked tunnel obtained, without any refuse, because the dust and rubbish are used on the spot in the form of a mortar which is more compact and more homogeneous than the soil traversed. The larva therefore works in the midst of clayey mire; and this is the cause of the stains that astonish us so much when we see it issuing from excessively dry soil. The perfect insect, though relieved henceforth from all mining labour, does not utterly abandon the use of its bladder; a few drains of urine are preserved as a weapon of defence. When too closely observed, it discharges a spray at the intruder and quickly flies away. In either form, the Cicada, his dry constitution notwithstanding, proves himself a skilled irrigator.