It is worth noting that there are no wingless Dragon-flies, and that none have developed unnecessary ornament in the form of spines, horns, or frills of any kind, such as are so commonly met with among groups of more sedentary habits like the Phasmidæ and the Beetles, for example. In other words, there is clearly a direct relation between ornament and the mode of life. It is also clear that some modes of subsistence are very inelastic, allowing of no more than very slight structural variations, for the Dragon-flies are an extremely ancient group. Fossil species of large size are known from the Lower Lias, and the remains of a giant measuring two feet in expanse of wings has been found in the Carboniferous. This species, however, seems to have stood near the parting of the ways between the May-flies and the Dragon-flies. But be this as it may, undoubtedly Dragon-flies hovered over the backs of sleeping Ichthyosaurs and furnished food for Pterodactyles millions of years ago, as they now hover over lazy kine for the sake of the flies forgathered there, or dodge to avoid the stoop of the Hobby, and in all this vast space of time they have not appreciably changed. And what is true of the Dragon-fly is true also of the May-fly, for it is clear that they are of the same stock. It is true at any rate in so far as the conformation of the body is concerned. The possibility that it may be equally true in regard to the details of their life-history almost staggers one, because these are, in many respects, of a quite remarkable character. As with the Dragon-fly, there is a prolonged period of larval life, lasting from one to two years, which time is passed in streams and pools where a luxuriant vegetation ensures a plentiful supply of food. Some are carnivorous, but in the majority of species minute plants only are eaten. More than forty species are to be reckoned as natives of the British Islands, the commonest being the “Green Drake” and “Grey Drake,” beloved by the fisherman. These names are applied, it may be mentioned, to the phase known as the sub-imago which precedes the fully-adult stage, of _Ephemera vulgata_ and _E. danica_.