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 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
