Let us leave the Leaf-cutter to finish depositing her eggs in other galleries, which will be colonized in the same manner, and consider for a moment her skill as a cutter. Her edifices consist of a multitude of fragments belonging to three categories: oval pieces for the sides of the cells; round pieces for the lids; and irregular pieces for the barricades at the front and back. The last present no difficulty: the Bee obtains them by removing from the leaf some projecting portion, as it stands, a serrate lobe which, owing to its notches, shortens the insect's task and lends itself better to scissor-work. So far, there is nothing to deserve attention: it is unskilled labour, in which an inexperienced apprentice might excel. With the oval pieces, it becomes another matter. What model has the Megachile when cutting her neat ellipses out of the delicate material for her wallets, the robinia-leaves? What mental pattern guides her scissors? What system of measurement tells her the dimensions? One would like to picture the insect as a living pair of compasses, capable of tracing an elliptic curve by a certain natural inflexion of its body, even as our arm traces a circle by swinging from the shoulder. A blind mechanism, the mere outcome of its organization, would alone be responsible for its geometry. This explanation would tempt me if the large oval pieces were not accompanied by much smaller ones, also oval, which are used to fill the empty spaces. A pair of compasses which changes its radius of its own accord and alters the curve according to the plan before it appears to me an instrument somewhat difficult to believe in. There must be something better than that. The circular pieces of the lid suggest it to us.