Let us look at the picture of a sting given on (_a_) Plate XIII., where is seen a sharp-pointed object surrounded by fleshy matter. This is the sting proper, and it is very smooth and hard, as well as being finely pointed. In order to give you some idea of this, I have mounted alongside a sting, one of the finest needles obtainable for comparison, and you will see the picture in (_b_) Plate XI. The needle is at the top, and looks like a great crowbar compared with the beautifully fine and tapering sting. This sting is really a sheath, or kind of case, in which are enclosed two needle-like darts. Its purpose is to protect the darts and also to make the actual wound. Outside the end of the sheath are two rows of three, or sometimes more barbs, which point backwards. Many of you, no doubt, have seen in our museums the spears and arrows used by savages, which have ugly barbs at their points. When the warrior runs the spear into an enemy, it does not slip out as it would do were the shaft just a plain one. The barbs on the outside of the sheath are used for this purpose, that is, to prevent the sheath from slipping out of the hole it has pierced, until the operation of stinging is completed. The darts enclosed in the sheath are capable of being moved up and down in it, by a powerful and complicated set of muscles. They act like drills, and when the sheath has made the first hole and, as it were, opened the way for them, the darts commence to travel up and down at a great rate. Every time they come down they go further into the flesh, and so make the hole deeper. They, too, have barbs which are more pronounced than those on the outside of the sheath, and so take a firmer hold on the flesh. You will clearly see these barbs on one of the darts in (_b_) Plate XIII. The darts themselves are hollow, and near each barb there is a tiny hole, which leads into the central hollow, down which the poison is poured. The hole made by the sharp little darts is not deep enough to cause the pain we feel when stung; this is due to the poison which is sent into the wound. This poison consists chiefly of formic acid, and is stored in the poison-bag which is shown on (_a_) Plate XIII. The poison is forced through the holes by two little pumps situated at the base of the sheath, and which are worked by the same muscles which move the darts. You will see from this that stinging is quite an elaborate process. First the sharp point of the sheath enters the flesh and is held there by its barbs. Then the darts work up and down, making the wound deeper and deeper, while the tiny pumps are forcing in the poison. So quickly does all this take place that the sheath is driven in up to the hilt and the wound filled with poison, long before we have time to knock the angry little insect away.