Many of the spirals have more than a single volute. It is as though one were to attach a number of very flexible rods to an axle, like spokes of a wheel without a rim and then revolve the axle rapidly. The flexible rods would bend under the rapid rotation, and form a series of spiral curves not unlike many of these nebulæ. Indeed, it is impossible to escape the conviction that these great celestial whorls are whirling around an axis. And it is most important in the study of the growth of worlds, to recognize that the type specimen is a revolving spiral. Therefore, the rotating flattened globe of incandescent matter postulated by Laplace's nebular hypothesis would make of our solar system an exceptional world, and not a type of stellar evolution in general. Keeler's photographs have taught us one thing more. Scarcely is there a single one of his negatives that does not show nebulæ previously uncatalogued. It is estimated that if this process of photography could be extended so as to cover the entire sky, the whole number of nebulæ would add up to the stupendous total of 120,000; and of these the great majority would be spiral. When we approach the question of the distribution of nebulæ in different parts of the sky, as shown by their catalogued positions, we are met by a curious fact. It appears that the region in the neighborhood of the Milky Way is especially poor in nebulæ, whereas these objects seem to cluster in much larger numbers about those points in the sky that are farthest from the Milky Way. But we know that the Milky Way is richer in stars than any other part of the sky, since it is, in fact, made up of stellar bodies clustered so closely that it is wellnigh impossible to see between them in the denser portions. Now, it cannot be the result of chance that the stars should tend to congregate in the Milky Way, while the nebulæ tend to seek a position as far from it as possible. Whatever may be the cause, we must conclude that the sidereal system, as we see it, is in general constructed upon a single plan, and does not consist of a series of universes scattered at random throughout space. If we are to suppose that nebulæ turn into stars as a result of condensation or any other change, then it is not astonishing to find a minimum of nebulæ where there is a maximum of stars, since the nebulæ will have been consumed, as it were, in the formation of the stars. [Illustration: The "Dumb-Bell" Nebula. Photographed by Keeler, July 31, 1899. Exposure, three hours.]