In the original spiral we have seen that, as a whole, it was of necessity pyriform in shape. The planets formed therefrom would thus be found to increase in size from within outward to a maximum, after which they would again decrease, but not to the original minimum, while the extreme outer planet would also be unduly enlarged by increment from partially dissipated terminal filaments, gradually attracted thereto from surrounding space. There is such an undue enlargement of the planet Neptune, and this, with its relatively compressed orbit, before alluded to, renders it almost certain that Neptune is in reality the outermost member of our planetary system. We find this gradation of size to be the case in our solar system, except where the series has been broken by the multitudinous separation, from violent internal repulsion, of one of the convolutions into parallel strands showing all sorts of perturbations, this being the convolution which occupied the region between the orbits of Mars and Jupiter, and which, by the coalescence of these numerous parallel strands into small planetary bodies, has filled the space with a belt of asteroids hundreds and perhaps thousands or even tens of thousands in number. It is probable that a law regulating the ellipticity of planetary orbits can be deduced from a consideration of the principles which have governed their inception, and with these are doubtless closely related those laws of Laplace which have demonstrated that "in any system of bodies travelling in one direction around a central attracting orb, the eccentricities and inclinations, if small at any one time, would always continue inconsiderable." (Appleton's Cyclopædia, article "Planet.") We have thus traced the genesis of a solar system from its earliest stages forward through its various changes until, complete and in working order, it is ready to be sent on its eternal course, either alone or as one of a vast congeries of similar systems, like the Milky Way. (See frontispiece for illustration of a series of types of development from a straight-tailed comet, through different curvatures, and spiral nebulæ of less and less divergence, until nearly circular, and finally terminating in a complete solar system.) These processes of creation may be isolated, or they may flash a hundred million solar systems into being together, as crystals flash forth in the rock; but, when once formed, they go forth each as eternal as space itself.