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.
So that we see, that though it has pleas'd the All-wise Creator, to indue this creature with such multitudes of eyes, yet has he not indued it with the faculty of seeing more then another creature; for whereas this cannot move his head, at least can move it very little, without moving his whole body, biocular creatures can in an instant (or the twinkling of an eye, which, being very quick, is vulgarly used in the same signification) move their eyes so as to direct the optick Axis to any point; nor is it probable, that they are able to see attentively at one time more then one Physical point; for though there be a distinct Image made in every eye, yet 'tis very likely, that the observing faculty is only imploy'd about some one object for which they have most concern.
Now, as we accurately distinguish the site or position of an Object by the motion of the Muscles of the eye requisite to put the optick Line in a direct position, and confusedly by the position of the imperfect Picture of the object at the bottom of the eye; so are these crustaceous creatures able to judge confusedly of the position of objects by the Picture or impression made at the bottom of the opposite Pearl, and distinctly by the removal of the attentive or observing faculty, from one Pearl to another, but what this faculty is, as it requires another place, so a much deeper speculation. Now, because it were impossible, even with this multitude of eye-balls, to see any object distinct (for as I hinted before, onely those parts that lay in, or very neer, the optick Lines could be so) the Infinitely wise Creator has not left the creature without a power of moving the head a little in Aerial crustaceous animals, and the very eyes also in crustaceous Sea-animals; so that by these means they are inabled to direct some optick line or other against any object, and by that means they have the visive faculty as compleat as any Animal that can move its eyes.
