It is time that we thought of experimenting. The Mason-bees intended for the journey must be marked with a sign whereby I may know them. A solution of gum arabic, thickened with a colouring-powder, red, blue or some other shade, is the material which I use to mark my travellers. The variety in hue will save me from confusing the subjects of my different experiments. When making my former investigations, I used to mark the Bees at the place where I set them free. For this operation, the insects had to be held in the fingers one after the other; and I was thus exposed to frequent stings, which smarted all the more for being constantly repeated. The consequence was that I was not always quite able to control my fingers and thumbs, to the great detriment of my travellers; for I could easily warp their wing-joints and thus weaken their flight. It was worth while improving the method of operation, both in my own interest and in that of the insect. I must mark the Bee, carry her to a distance and release her, without taking her in my fingers, without once touching her. The experiment was bound to gain by these nice precautions. I will describe the method which I adopted. The Bee is so much engrossed in her work when she buries her abdomen in the cell and rids herself of her load of pollen, or when she is building, that it is easy, at such times, without alarming her, to mark the upper side of the thorax with a straw dipped in the coloured glue. The insect is not disturbed by that slight touch. It flies off; it returns laden with mortar or pollen. You allow these trips to be repeated until the mark on the thorax is quite dry, which soon happens in the hot sun necessary to the Bee's labours. The next thing is to catch her and imprison her in a paper bag, still without touching her. Nothing could be easier. You place a small test-tube over the Bee engrossed in her work; the insect, on leaving, rushes into it and is thence transferred to the paper bag, which is forthwith closed and placed in the tin box that will serve as a conveyance for the whole party. When releasing the Bees, all you have to do is open the bags. The whole performance is thus effected without once giving that distressing squeeze of the fingers.