9. But even if the supposed spectator attended only to the obvious and superficial resemblances between one of the planets and another, he might still, if he were acquainted with the general economy of the Universe, have great hesitation in inferring that, if one of them were inhabited, the others also must be inhabited. For, as we have said, in the plan of creation, we have a profusion of examples, where similar visible structures do not answer a similar purpose; where, so far as we can see, the structure answers no purpose in many cases; but exists, as we may say, for the sake of similarity: the similarity being a general Law, the result, it would seem, of a creative energy, which is wider in its operation than the particular purpose. Such examples are, as we have said, the finger-bones which are packed into the hoofs of a horse, or the paps and nipples of a male animal. Now the spectator, recollecting such cases might say: I know that the earth is inhabited; no doubt Mars and Jupiter are a good deal like the Earth; but are they inhabited? They look like the terrestrial breast of Nature: but are they really nursing breasts? Do they, like that, give food to living offspring? Or are they mere images of such breasts? male teats, dry of all nutritive power? sports, or rather overworks of nature; marks of a wider law than the needs of Mother Earth require? many sketches of a design, of which only one was to be executed? many specimens of the preparatory process of making a Planet, of which only one was to be carried out into the making of a World? Such questions might naturally occur to a person acquainted with the course of creation in general; even before he remarked the features which tend to show that Jupiter and Saturn, that Venus and Mercury, have not been developed into peopled worlds, like our Earth. 10. Perhaps it may be said, that to hold this, is to make Nature work in vain; to waste her powers; to suppose her to produce the frame work, and not to build; to make the skeleton, and not to clothe it with living flesh; to delude us with appearances of analogy and promises of fertility, which are fallacious. What can we reply to this?