This we may be sure of, that the filaments or sensative parts of the Retina must be most exceedingly curious and minute, since the whole Picture it self is such; what must needs the component parts be of that Retina, which distinguishes the part of an object’s Picture that must be many millions of millions less then that in a man’s eye?  And how exceeding curious and subtile must the component parts of the medium that conveys light be, when we find the instrument made for its reception or refraction to be so exceedingly small? we may, I think, from this speculation be sufficiently discouraged from hoping to discover by any optick or other instrument the determinate bulk of the parts of the medium that conveys the pulse of light, since we find that there is not less accurateness shewn in the Figure and polish of those exceedingly minute lenticular surfaces, then in those more large and conspicuous surfaces of our own eyes.  And yet can I not doubt, but that there is a determinate bulk of those parts, since I find them unable to enter between the parts of Mercury, which being in motion, must necessarily have pores, as I shall elsewhere shew, and here pass by, as being a digression.

As concerning the horns FF, the feelers or smellers, GG, the Probascis HH, and I, the hairs and brisles, KK, I shall indeavour to describe in the 42. Observation.

* * * * *

Observ.  XL. Of the Teeth of a Snail_._

I have little more to add of the Teeth of a Snail, besides the Picture of it, which is represented in the first Figure of the 25. Scheme, save that his bended body, ABCDEF, which seem’d fashioned very much like a row of small teeth, orderly plac’d in the Gums, and looks as if it were divided into several smaller and greater black teeth, was nothing but one small bended hard bone, which was plac’d in the upper jaw of the mouth of a House-Snail, with which I observ’d this very Snail to feed on the leaves of a Rose-tree, and to bite out pretty large and half round bits, not unlike the Figure of a (C) nor very much differing from it in bigness, the upper part ABCD of this bone, I found to be much whiter, and to grow out of the upper chap of the Snail, GGG, and not to be any thing neer so much creas’d as the lower and blacker part of it HIIHKKH which was exactly shap’d like teeth, the bone growing thinner, or tapering to an edge towards KKK.  It seem’d to have nine teeth, or prominent parts IK, IK, IF, &c. which were join’d together by the thinner interpos’d parts of the bone.  The Animal to which these teeth belong, is a very anomalous creature, and seems of a kind quite distinct from any other terrestrial Animal or Insect, the Anatomy whereof exceedingly differing from what has been hitherto given of it I should have inserted, but that it will be more proper in another place.  I have never met with any kind of Animal whose teeth are all join’d in one, save onely that I lately observ’d, that all the teeth of a Rhinocerot, which grow on either side of its mouth, are join’d into one large bone, the weight of one of which I found to be neer eleven pound Haverdupois.  So that it seems one of the biggest sort of terrestrial Animals, as well as one of the smallest, has his teeth thus shap’d.