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Hooke, Robert, 1635-1703 / Micrographia: or some physiological descriptions of minute bodies made by magnifying glasses : with observations and inquiries thereupon
(MDCLXVII [1667])

Observ. XXXIX. Of the eyes and head of a grey drone-fly, and of several other creatures,   pp. 175-180


Page 178


              MICROGRAPHI A.
  Thirdly,that thofe which they call the eyes of CrabsLobftersShrimps,
and the like, and are really fo, are Hefijp'her'd, almoft in the fame man-
ner as thefe of Flies are. And that they really are fo, I have very often
try'd, by cutting off thefe little movable knobs, and putting the creature
again into the water, that it would fwim to and fro, and move up and
down as well as before, but would often hit it felf againft the rocks or
tones; and though I put my hand juft before its head, it would not at
all hart or fly back till I touch'd it, whereas whilfi thofe were remain-
ing, it would htart back,and avoid my hand or a [tick at a good diftance
before it touch'd it. And if in cruifaccous Sea-animals, then it feems very
probable alfo,that thefe knobs are the eyes in crufiaceowInfects, which are
alfo of the fame kind, onely in a higher and more aftive Element; this the
conformity or congruity of many other parts common to either of them,
will hrongly argue their crujiaceo(u armourtheir number of leggs,which
are fix, betide the two great claws, wvhich anfiwver to the wings in Infeas
;
and in all kind of Spiders, as alfo in many other Infe~ts that want wings,
we fhall find the compleat number of them, and not onely the number,
but the very ihape, figure, joints, and claws of Lobfters and Crabs, as is
evident in Scorpions and Spiders, as is vifible in the fecond Figure ofthe
3 i. scheme,and in the little Mite-worm,which I call a Land-crab,defcrib'd
in the fecond Figure of the 3 3. scheme ,but in their manner of generation
being oviparous, &c. And it were very worthy observation, whether
there be not fome kinds of transformation and metamor'phofis in the fe-
veral htates of crufiaceous water-animals, as there is in feveral forts of
In-
fefts ; for if fuch could be met with,the progrefs of the variations would
be much more conspicuous in thofe larger Animals, then they can be in
any kind of InfeCis our colder Climate affords.
   Thefe being their eyes, it affords us a very pretty Speculation to con-
 template their manner of vifion, which, as it is very differing from that
of
 biocular Animals, fo is it not lefs admirable.
   That each of thefe Pearls or HexiJpheres is a perfedt eye, I think we
 need not doubt, if we confider onely the outfide or figure of any one of
 them, for they being each of them cover'd with a tranfparent protube-
 rant Cornea, and containing a liquor within them, refembling the watry
 or glaflie humours of the eye, muft neceflarily refra& all the parallel
 Rays that fall on them out of the air, into a point not farr diftant within
 them, where (in all probability) the Retina of the eye is placed,and that
 opacous, dark, and mucous inward coat that (I formerly fbew'd) I found
 to fubtend the concave part of the clufter is very likely to be that tu-
 nicle or coat, it appearing through the Micrjc/ope to be plac'd a little
 more than a Diameter ofthofe Pearls below or within the ttnica cornea.
 And if fo, then is there in all probability, a little PiCture or Image of
the
 objeCts without, painted or made at the bottom of the Retina againft
 every one of thofe Pearls, fo that there are as many impreffions on the
 Retina or opacous 1kin, as there are Pearls or HemiJpheres on the clufher.
 But becaufe it is impollible for any protuberant furface whatfoever, whe-
 therfphtrial or other, fo to refraCt the Rays that come from farr remote
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