Though there is a great deal of Pleasure in contemplating the material World, by which I mean that System of Bodies into which Nature has so curiously wrought the Mass of dead Matter, with the several Relations which those Bodies bear to one another; there is still, methinks, something more wonderful and surprizing in Contemplations on the World of Life, by which I mean all those Animals with which every Part of the Universe is furnished. The Material World is only the Shell of the Universe: The World of Life are its Inhabitants.
If we consider those parts of the Material World which lie the nearest to us, and are therefore subject to our Observations and Enquiries, it is amazing to consider the Infinity of Animals with which it is stocked. Every part of Matter is peopled: Every green Leaf swarms with Inhabitants. There is scarce a single Humour in the Body of a Man, or of any other Animal, in which our Glasses do not discover Myriads of living Creatures. The Surface of Animals is also covered with other Animals, which are in the same manner the Basis of other Animals, that live upon it; nay, we find in the most solid Bodies, as in Marble it self, innumerable Cells and Cavities that are crouded with such imperceptible Inhabitants, as are too little for the naked Eye to discover. On the other hand, if we look into the more bulky parts of Nature, we see the Seas, Lakes and Rivers teeming with numberless kinds of living Creatures: We find every Mountain and Marsh, Wilderness and Wood, plentifully stocked with Birds and Beasts, and every part of Matter affording proper Necessaries and Conveniencies for the Livelihood of Multitudes which inhabit it.
The Author of the Plurality of Worlds  draws a very good Argument from this Consideration, for the peopling of every Planet; as indeed it seems very probable from the Analogy of Reason, that if no Part of Matter, which we are acquainted with, lies waste and useless, those great Bodies which are at such a Distance from us should not be desart and unpeopled, but rather that they should be furnished with Beings adapted to their respective Situations.
Existence is a Blessing to those Beings only which are endowed with Perception, and is in a manner thrown away upon dead Matter, any further than as it is subservient to Beings which are conscious of their Existence. Accordingly we find, from the Bodies which lie under our Observation, that Matter is only made as the Basis and Support of Animals, and that there is no more of the one, than what is necessary for the Existence of the other.
Infinite Goodness is of so communicative a nature, that it seems to delight in the conferring of Existence upon every Degree of [Perceptive ] Being. As this is a Speculation, which I have often pursued with great Pleasure to my self, I shall enlarge farther upon it, by considering that part of the Scale of Beings which comes within our Knowledge.
There are some living Creatures which are raised but just above dead Matter. To mention only that Species of Shell-fish, which are form'd in the Fashion of a Cone, that grow to the Surface of several Rocks, and immediately die upon their being sever'd from the Place where they grow. There are many other Creatures but one Remove from these, which have no other Sense besides that of Feeling and Taste. Others have still an additional one of Hearing; others of Smell, and others of Sight. It is wonderful to observe, by what a gradual Progress the World of Life advances through a prodigious Variety of Species, before a Creature is form'd that is compleat in all its Senses; and even among these there is such a different Degree of Perfection in the Sense which one Animal enjoys beyond what appears in another, that though the Sense in different Animals be distinguished by the same common Denomination, it seems almost of a different Nature. If after this we look into the several inward Perfections of Cunning and Sagacity, or what we generally call Instinct, we find them rising after the same Manner, imperceptibly one above another, and receiving additional Improvements, according to the Species in which they are implanted. This Progress in Nature is so very gradual, that the most perfect of an inferior Species comes very near to the most imperfect of that which is immediately above it.
The exuberant and overflowing Goodness of the Supreme Being, whose Mercy extends to all his Works, is plainly seen, as I have before hinted, from his having made so very little Matter, at least what falls within our Knowledge, that does not swarm with Life: Nor is his Goodness less seen in the Diversity, than in the Multitude of living Creatures. Had he only made one Species of Animals, none of the rest would have enjoyed the Happiness of Existence; he has, therefore, specified in his Creation every degree of Life, every Capacity of Being. The whole Chasm in Nature, from a Plant to a Man, is filled up with diverse Kinds of Creatures, rising one over another, by such a gentle and easy Ascent, that the little Transitions and Deviations from one Species to another, are almost insensible. This intermediate Space is so well husbanded and managed, that there is scarce a degree of Perception which does not appear in some one part of the World of Life. Is the Goodness, or Wisdom of the divine Being, more manifested in this his Proceeding?
There is a Consequence, besides those I have already mentioned, which seems very naturally deducible from the foregoing Considerations. If the Scale of Being rises by such a regular Progress, so high as Man, we may by a parity of Reason suppose that it still proceeds gradually through those Beings which are of a Superior Nature to him; since there is an infinitely greater space and room for different Degrees of Perfection, between the Supreme Being and Man, than between Man and the most despicable Insect. This Consequence of so great a variety of Beings which are superior to us, from that variety which is inferior to us, is made by Mr. Lock, in a Passage which I shall here set down, after having premised, that notwithstanding there is such infinite room between Man and his Maker for the Creative Power to exert it self in, it is impossible that it should ever be filled up, since there will be still an infinite Gap or Distance between the highest created Being, and the Power which produced him.
That there should be more Species of intelligent Creatures above us, than there are of sensible and material below us, is probable to me from hence; That in all the visible corporeal World, we see no Chasms, or no Gaps. All quite down from us, the descent is by easy steps, and a continued Series of things, that in each remove differ very little one from the other. There are Fishes that have Wings, and are not Strangers to the airy Region: and there are some Birds, that are Inhabitants of the Water; whose Blood is cold as Fishes, and their Flesh so like in taste, that the Scrupulous are allowed them on Fish-days. There are Animals so near of kin both to Birds and Beasts, that they are in the middle between both: Amphibious Animals link the Terrestrial and Aquatick together; Seals live at Land and at Sea, and Porpoises have the warm Blood and Entrails of a Hog; not to mention what is confidently reported of Mermaids or Sea-Men. There are some Brutes, that seem to have as much Knowledge and Reason, as some that are called Men; and the Animal and Vegetable Kingdoms are so nearly join'd, that if you will take the lowest of one, and the highest of the other, there will scarce be perceived any great difference between them: and so on till we come to the lowest and the most inorganical parts of Matter, we shall find every where that the several Species are linked together, and differ but in almost insensible degrees. And when we consider the infinite Power and Wisdom of the Maker, we have reason to think that it is suitable to the magnificent Harmony of the Universe, and the great Design and infinite Goodness of the Architect, that the Species of Creatures should also, by gentle degrees, ascend upward from us towards his infinite Perfection, as we see they gradually descend from us downwards: Which if it be probable, we have reason then to be persuaded, that there are far more Species of Creatures above us, than there are beneath; we being in degrees of Perfection much more remote from the infinite Being of God, than we are from the lowest State of Being, and that which approaches nearest to nothing. And yet of all those distinct Species, we have no clear distinct Ideas. 
In this System of Being, there is no Creature so wonderful in its Nature, and which so much deserves our particular Attention, as Man, who fills up the middle Space between the Animal and Intellectual Nature, the visible and invisible World, and is that Link in the Chain of Beings, which has been often termed the nexus utriusque Mundi. So that he who in one respect is associated with Angels and Arch-Angels, may look upon a Being of infinitei Perfection as his Father, and the highest Order of Spirits as his Brethren, may in another respect say to Corruption, thou art my Father, and to the Worm, thou art my Mother and my Sister. 
[Footnote 1: Fontenelle, Entretiens sur la Pluralité des Mondes. Troisième Soir.]
[Footnote 2: [Preceptive] and in first reprint.]
[Footnote 3: Essay concerning Human Understanding, Bk. III. ch. vi. § 12.]
[Footnote 4: Job. xvii. 14.]Translation of motto: