26 The B-@ © K of N Ay WOR) B story 
till they at laft come to lofe even their exter- 
nal form. — 
In examining a Loufe by the microfcope, its 
white veins and other internal parts appear, 
as likewife a moft wonderful motion in its in- 
teftines, on account of the tranfparency of the 
internal parts of this infe@. When the Loufe 
feeds, the blood is feen to rufh’like a torrent 
into the ftomach, and its greedinefs is fo great, 
that the excrements contained in the inteftines, 
are ejected at the fame time, to make room 
for this new fupply. But I thall treat of 
thefe infects in particular, as foon as I hall 
have finifhed what I propofe faying in general 
of thefe that belong to the firft order. 
What I have already mentioned is but by 
way of parenthefis, that my countrymen might 
know fomething of the ftupendous aétions and 
conftructions of fo {mall an animal, and be 
thereby incited to praife the author of nature, 
who has here placed in one point of view fo 
many and fo great wonders, ‘The great ufeful- 
nels of the microfcope will alfo appear from 
the preceding obfervations, fince, by difcover- 
ing tousthe mutfcles, veffels, and internal parts 
of fo {mall an infect, it acquaints us with the 
incomprehenfible perfections of that great 
being, who could not only create, but im- 
part life and motion to fo minute organs. There 
is another advantage alfo in microfcopes, viz. 
that in tranfparent animals, they give us a much 
more perfect knowledge of the motion of their 
inteftines, than any we can obtain in other 
creatures by diffecting them. This benefit of 
the microfcope has been already taken notice 
of by the illuftrious Hooke, in his Microgra- 
phia, or collection of obfervations made with 
microfcopes, a work lately publifhed in Eng- 
lith, and dedicated to his Britannick majefty. 
I have reafon to believe, but for want of 
fufficient experiments I dare not as yet affirm, 
that the Lice of other fanguiferous animals, and 
the Lice of infects, with thofe that live upon 
plants, or ramble about the fields, belong to 
the laft mentioned order or clafs*. Mean 
time it will appear evident, in treating of the 
fourth clafs, that there are fome tree Lice, def- 
cribed by me under the title of animalcules, 
found in the excrefcences of the black poplar, 
which belong to the fecond order: 
Neither can I affirm, that the Tick, or Ri- 
cinus of Aldrovandus, though placed by me 
in this clafs, does really belong to it; though 
I have in my colle&ion a good f{pecimen of 
this infect. 
I likewife refer the Bug which lies in bed- 
fteads and furniture to this firft clafs; as alfo 
the Crab-Loufe, though I have not as yet 
made experiments fufficient to determine per- 
fectly the nature of this laft infea@. 
I have alfo in my collection the Loufe of 
the Whale, which is almoft an inch long, and 
half an inch broad, of a very fingular form, 
and all over covered with a fhell -. 
After thefe, I rank the Flea t in the firft 
clafs. This infect alfo fprings from a Nit, in the 
which it elegantly changes to a red colour, 
like other infects in the Nymph ftate; the 
changes it undergoes, while as yet in the 
{tate of the Nit, and the manner in which 
it from white becomes black, are eafily difcern- 
able by the help of the microfcope: nor are 
thefe obfervations of little ufe or importance, 
as I {hall hereafter prove at a proper feafon. 
I have been told that Dotor Lewenhoeck 
obferved a Flea at Delft, which, about the end 
of fummer, iffued from an egg in form of a 
Worm, and then fhut itfelf up in a cafe till 
the enfuing month of March; but I thall not 
as yet affirm the certainty of this obfervation ; 
neither fhall I determine whether the Flea wore 
in its cafe the figure of a Chryfalis, or a 
Nymph ; if it did, the infe& muft belong to 
the third, and by no means to the firft order. 
I fhall ufe the firft opportunity of exactly ob- 
ferving this infect, fo as to know the certainty 
of what has been advanced concerning it, as 
fuch enquiry cannot be attended with any great 
trouble §. 
I likewife place in this firft clafs an infec 
which is generally found in cifterns where — 
rain water is kept, and which Goedaert has 
defcribed by the name of the Water-Loufe, as 
may be feen in the third volume, letter X. But 
as the ftructure and difpofitions of this little 
animal differ greatly from thofe of the com- 
* Redi, who very accurately examined this fubject, found Lice upon the Lion and the Tiger. He calls all thofé on quadru- 
pedes by this name; and thofe on birds, Fleas; but heis in this miftaken, the diftinctive characters are to be found in the ftruc- 
ture of the parts, not on the creatures whereon they feed. The fame author obferves, that the Lice bear no proportion to the 
bignefs of the creature on which they live, the Starling having a Loufe as large as that of the Swan. 
+ The common Fly is fubje& to a particular infeé&t which lives upon his head ; this is fo minute that few have obferved it ; 
its fize is calculated by La Hire of the French academy, to be not more than a four thoufandth part of that of the head of 
the Fly. This is of the Acarus kind, having eight legs. ' 
‘The Crab-Loufe upon the human body is of the fame genus with the common one of the head, but a different fpecies. It 
is deftroyed by mixtures with water, in which crude mercury is boiled. 
Even the Snail is fubject to be infefted with a kind of Loufe, but in a very fingular manner; for this creature, which has 
eight legs, and is of the Acarus kind, lives equally on the furface of the body, and within the inteftines, running in and out 
at its pleafure. It is ufually feen alive in the intefines, when they are examined by the microfcope. _ { 
{ The common Flea is an extremely fingular infect, there being no other fpecies properly of its kind: the generical cha- 
racters are thefe; it has fix legs formed for leaping, the eyes are only two, the organ which ferves for a mouth is bent down- 
wards, and the belly is roundifh and comprefled. Only the Flea of the human body has thefe charafters ; what is called the 
Pulex Sturni is an Acarus, and the-reft of the infeéts which have received this name from inaccurate obfervations, belong to- 
other genera, 
§ Though the Flea is peculiar in the human kind, it is not fo with the Lonfe. Multitudes of animals, birds and beafts, are in- 
fefted with Lice, and though of different fpecies upon moft kinds, they all have the charaéters here defcribed, and are pro- 
perly of the Pediculus or Loufe kind, Infects have alfo leffer infects living upon them, particularly the Beetle ; but though thefe 
are called Lice, from their living on other animals, they are not of that kind. The Loufe of the Beetle, as it is commonly 
called, has eight legs, whereas the proper Loufe has but fix: this creature is properly an Acarus, and fo of the other. 
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