4.0 
or to fuch advantage, as in the Oviducts of the 
female Fly, opened for this purpofe; and, no 
doubt, the moft certain method of invefti- 
gating the eggs of infects, fo as to obtain fome 
certain knowledge concerning them, is that by 
diffection of the infects; but then the open- 
ing of thefe fmall animals at the exact time, 
when their eggs are perfect in the Ovary, and 
ready for laying, depends entirely upon chance, 
I have a fall box full of infeat’s eggs in 
my collection, fo very curious, that I fhould 
not think a particular treatife ill beftowed upon 
them ; for they all greatly differ from one an- 
other in fhape and colour. Some are oblong, 
others oval; fome again perfectly round, others 
angular; fome pear-fhaped, fome like the feed 
of the carduus benedictus, and others of other 
forms. There is alfo the -greateft variety of 
colours amongft them; white, yellow, red, 
fky-coloured, green ; and in fome is to be feen 
a beautiful mixture of feveral colours, fo as to 
make it almoft impoffible to give a particular 
account of them. Some alfo are foft, others 
hard; fome are only covered with a flight 
membrane, whilft others have a fhell, or frm 
cruft, like parchment. Again, fome are fhel- 
tered by a froth that furrounds them, others 
are covered with hair: fome are found faftened 
by a vifcous matter to the branches of trees, fo 
_as to form a ring about them; others lie fingly, 
and at random. Some ftand clofe to each other 
upon their ends; others lie parallel to the ho- 
rizon; and fome are found buried in animal 
and vegetable fubftances, whilft others are only 
laid-in a loofe manner upon the furfaces of 
fuch things. 
ye PiGa ates 
I here lay before the reader a figure of a 
Worm, which changes to the boghoufe Fly, 
as it appears when magnified by the micro- 
{cope. We may clearly difcern in it thofe an- 
nular divifions, of which fome conftitute its 
head, the next to them the thorax, and the 
hindmoft the creature’s abdomen and tail. The 
circumference of every part of the body ap- 
pears adorned with feveral, as it were, promi- 
nent feathered bandages. But the infect lofes 
the advantages of thefe as ornaments, becaufe 
it cannot but foul them, by crawling through 
the offenfive matter upon which it feeds. For 
this reafon it ought to be well wathed, in order 
to become fit for a microfcopical obfervation : 
nor need we fear to do it any injury, by treat- 
ing it in this manner ; for it has a {trong con- 
ftitution. Befides, this Worm is one of the 
fpecies of infects which have a hard fkin, the 
better to refift the acrimony of the putrefcent 
juices, amongft which it lives. ‘This hardnefs 
of the boghoufe Worm’s fkin, is the caufe of 
its not lofing its external form, when it changes 
to a Nymph. 
EF LGiy, 
It muft be here very thoroughly confidered, 
that thefe Worms, on their afluming the fhape 
of Vermiform-Nymphs, become motionlefs, 
and foon after draw up their fnout within the 
head; by which, and by a contraction of all 
Th BOOK of NATURE; or, 
the rings of their body towards each other, 
they become fhorter, in fo confiderable a de- 
gree, as may be feen in the fourth figure now 
before us: which likewife thews, that there is 
but little difference between the Worm repre~ 
fented in the third figure, and the Vermiform- 
Nymph exhibited in this place. The only dif- 
ference is this, that the Nymph is without any 
motion, whereas the Werm moves itfelf very 
brifkly, The drawing in of the fnout in the 
Nymph, {carce makes any difference; for the 
Worm itfelf is very often obferved to do the 
fame thing. But we muft here take {pecial 
notice, that all the Worms of this fourth order 
are not all changed to Nymphs, in the fame 
manner with the {pecimen of that order; which 
I here explain: neither do all the Nymphs 
equally exhibit the former limbs of their re= 
{pective Worms; the only reafon of which 
diverfity I take to be this, that fome of thefe 
Worms have a more delicate fkin than others, 
and confequently it is better adapted to con- 
form itfelf to the fhape of the latent Nymph, 
when the infe&ts change into that condition. 
This I fhall demonftrate in the ninth and tenth 
figures, by two particular and very evident 
examples, which will fupply us with a rule to 
judge by, in every cafe of the like nature. 
There is one circumftance more worth our 
notice in the Nymph, whofe figure we are now 
confidering: this is, that I have reprefented its 
fore-parts, about the head, fomewhat whiter 
and brighter than the reft of the body; becaufe 
the hidden Nymph, by the infenfible evapora- 
tion of its moifture, gradually contracts itfelf 
. more in this part than elfewhere, fo.as to leave - 
a vacant {pace, which, by affording a free paf- 
fage to the rays of light, thereby, in reality, 
acquires an extraordinary degree of brightneds, 
This particular I took notice of in a Nymph, 
like this Iam now defcribing, of the Mufca 
Afilus, or Gadfly, whofe hiftory follows this. 
It is likewife plain, that the empty part of the 
{kin, in the foregoing Nymph, may be dexter- 
oufly cut off with fciffors, without wounding 
the enclofed infect; and, upon doing fo, we 
may fee that the Nymph’s head lies in the fore- 
region of the Worm’s fkin; and that its eyes, 
which, in the beginning of the change, were 
of a milky white, are at this time turned to a 
purplith red. However, this experiment ought 
only to be tried upon Nymphs which are feveral 
days old; for we fhould certainly injure thofe 
that were younger, in the operation. It hap- 
pens in this Worm, as it does in all others of 
the fourth order, that the thorax conftantly 
continues the fame in the Nymph-ftate, with- 
out any vifible alteration : in’ the fame manner, 
as in Worms and Caterpillars of all the other 
orders, the legs, {pringing from the thorax, 
never change their fituation. But this laft cir- 
cumftance chiefly obtains in the fecond order, 
of which there are a great number of infects, 
whofe thorax, and efpecially the legs belong- 
ing to this part, do not fuffer the leaft altera- 
tion; that is, they neither grow longer or fhorter 
at the periods of the infects cafting their fkins. 
5 Fic, 
