What keeps them down, then, in the end to their average number? What prevents the development of the whole seven hundred? The simple answer is, continuous starvation. As usual, nature works with cruel lavishness. There are just as many spiders at any given minute as there are insects enough in the world or in their area to feed upon. Every spider lays hundreds of eggs, so as to make up for the average infant mortality by starvation, or by the attacks of ichneumon flies, or by being eaten themselves in the young stage, or by other casualties. And so with all other species. Each produces as many young on the average as will allow for the ordinary infant mortality of their kind, and leave enough over just to replace the parents in the next generation. And that's one of the reasons why it's no use punishing Lucy and Eliza for their misdeeds in this world. Kill them off if you will, and before next week a dozen more like them will dispute with one another the vacant place you have thus created in the balanced economy of that microcosm the garden. Our observations upon Lucy and Eliza, however, had the effect of making us take an increased interest thenceforth in spiders in general, which till that time we had treated with scant courtesy, and set us about learning something as to the extraordinary variety of life and habit to be found within the range of this single group of arthropods, at first sight so extremely alike in their shapes, their appearance, their morals, and their manners. It's perfectly astonishing, though, when one comes to look into it in detail, how exceedingly diverse spiders are in their mode of life, their structure, and the variety of uses to which they put their one extremely distinctive structural organ, the spinnerets. I will only say here that some spiders use these peculiar glands to form light webs by whose aid, though wingless, they float balloon-wise through the air; that others employ them to line the sides of their underground tunnels, and to make the basis of their marvellously ingenious earthen trap-doors; that yet others have learnt how to adapt these same organs to a subaquatic existence, and to fill cocoons with air, like miniature diving bells; while others, again, have taught themselves to construct webs thick enough to catch and hold even creatures so superior to themselves in the scale of being as humming-birds and sunbirds. This extraordinary variety in the utilization of a single organ teaches once more the same lesson which is impressed upon us elsewhere by so many other forms of organic evolution: whatever enables an animal or plant to gain an advantage over others in the struggle for life, no matter in what way, is sure to survive, and to be turned in time to every conceivable use of which its structure is capable, in the infinite whirligig of ever-varying nature. MUD.