First, that this outward skin, like the Cornea of the eyes of the greater Animals, was both flexible and transparent, and seem’d, through the Microscope perfectly to resemble the very substance of the Cornea of a man’s eye; for having cut out the cluster, and remov’d the dark and mucous stuff that is subjacent to it, I could see it transparent like a thin piece of skin, having as many cavities in the inside of it, and rang’d in the same order as it had protuberances on the outside, and this propriety, I found the same in all the Animals that had it, whether Flies or Shell-Fish.

Secondly, I found that all Animals that I have observ’d with those kind of eyes; have within this Cornea, a certain cleer liquor or juice, though in a very little quantity, and,

I observ’d thirdly, that within that cleer liquor, they had a kind of dark mucous lining, which was all spread round within the cavity of the clutter, and seem’d very neer adjoining to it, the colour of which, in some Flies, was grey; in others, black, in others red; in others, of a mix’d colour; in others, spotted; and that the whole clusters, when look’d on whilst the Animal was living, or but newly kill’d, appear’d of the same colour that this coat (as I may so call it) appear’d of, when that outward skin, or Cornea, was remov’d.

Fourthly, that the rest of the capacity of the clusters was in some, as in Dragon Flies, &c. hollow, or empty; in others fill’d with some kind of substance; in blue Flies, with a reddish musculous substance, with fibres tending from the center or bottom outwards; and divers other, with various and differing kinds of substances.

That this curious contrivance is the organ of sight to all those various Crustaceous Animals, which are furnish’d with it, I think we need not doubt, if we consider but the several congruities it has with the eyes of greater creatures.

As first, that it is furnish’d with a Cornea, with a transparent humour, and with a uvea or retina, that the Figure of each of the small Hemispheres are very Spherical, exactly polish’d, and most vivid, lively and plump, when the Animal is living, as in greater Animals, and in like manner dull, flaccid, and irregular, or shrunk, when the Animal is dead.

Next, that those creatures that are furnish’d with it, have no other organs that have any resemblance to the known eyes of other creatures.

Thirdly, that those which they call the eyes of Crabs, Lobsters, Shrimps, and the like, and are really so, are Hemispher’d, almost in the same manner as these of Flies are. And that they really are so, I have very often try’d, by cutting off these little movable knobs, and putting the creature again into the water, that it would swim to and fro, and move up and down as well as before, but would often hit it self against the rocks or stones; and though I put my hand just before its head, it would not at all start or fly back till I touch’d it, whereas whil’st those were remaining, it would start back, and avoid my hand or a stick at a good distance before it touch’d it. And if in crustaceous Sea-animals, then it seems very probable also, that these knobs are the eyes in crustaceous Insects, which are also of the same kind, onely in a higher and more active Element; this the conformity or congruity of many other parts common to either of them, will strongly argue, their crustaceous armour, their number of leggs, which are six, beside the two great claws, which answer to the wings in Insects; and in all kind of Spiders, as also in many other Insects that want wings, we shall find the compleat number of them, and not onely the number, but the very shape, figure, joints, and claws of Lobsters and Crabs, as is evident in Scorpions and Spiders, as is visible [Schem. 31.]
Fig. 2.
[Schem. 33.]
Fig. 2. in the second Figure of the 31. Scheme, and in the little Mite-worm, which I call a Land-crab, describ’d in the second Figure of the 33. Scheme, but in their manner of generation being oviparous, &c. And it were very worthy observation, whether there be not some kinds of transformation and metamorphosis in the several states of crustaceous water-animals, as there is in several sorts of Insects; for if such could be met with, the progress of the variations would be much more conspicuous in those larger Animals, then they can be in any kind of Insects our colder Climate affords.

These being their eyes, it affords us a very pretty Speculation to contemplate their manner of vision, which, as it is very differing from that of biocular Animals, so is it not less admirable.

That each of these Pearls or Hemispheres is a perfect eye, I think we need not doubt, if we consider onely the outside or figure of any one of them, for they being each of them cover’d with a transparent protuberant Cornea, and containing a liquor within them, resembling the watry or glassie humours of the eye, must necessarily refract all the parallel Rays that fall on them out of the air, into a point not farr distant within them, where (in all probability) the Retina of the eye is placed, and that opacous, dark, and mucous inward coat that (I formerly shew’d) I found to subtend the concave part of the cluster is very likely to be that tunicle or coat, it appearing through the Microscope to be plac’d a little more than a Diameter of those Pearls below or within the tunica cornea. And if so, then is there in all probability, a little Picture or Image of the objects without, painted or made at the bottom of the Retina against every one of those Pearls, so that there are as many impressions on the Retina or opacous skin, as there are Pearls or Hemispheres on the cluster. But because it is impossible for any protuberant surface whatsoever, whether sphærial or other, so to refract the Rays that come from farr remote lateral points of any Object as to collect them again, and unite them each in a distinct point, and that onely those Rays which come from some point that lies in the Axis of the Figure produc’d, are so accurately refracted to one and the same point again, and that the lateral Rays, the further they are remov’d, the more imperfect is their refracted confluence; It follows therefore, that onely the Picture of those parts of the external objects that lie in, or neer, the Axis of each Hemisphere, are discernably painted or made on the Retina of each Hemisphere, and that therefore each of them can distinctly sensate or see onely those parts which are very neer perpendicularly oppos’d to it, or lie in or neer its optick Axis. Now, though there may be by each of these eye-pearls, a representation to the Animal of a whole Hemisphere in the same manner as in a man’s eye there is a picture or sensation in the Retina of all the objects lying almost in an Hemisphere; yet, as in a man’s eye also, there are but some very few points which liyng in, or neer, the optick Axis are distinctly discern’d: So there may be multitudes of Pictures made of an Object in the several Pearls, and yet but one, or some very few that are distinct; The representation of any object that is made in any other Pearl, but that which is directly, or very neer directly, oppos’d, being altogether confus’d and unable to produce a distinct vision.