The tail forves the larva both for the purpofes o f Iwimming
and breathing, and it receives through the tail that which is the
univerfal principle o f life and motion in animals. By means of
thefe hairs it can flop ltfolf at pleafore when iwimming or
remain fufpended quietly in the water for any length o f time.
The motion o f this infect in fwimming is very beautiful, efpe-
cially when it advances with it’s whole body floating on the fur-
face o f the water, after filling itfelf with air by the tail. T o fet
* out, it firft bends the body to the right or left, and then contrafts
it in the form o f the letter S, and again ftretches it out in a
ftrait line: by thus alternately contrafting and then extending the
body, it moves along on the furface o f the water. It is of a very
quiet difpofition, and not difturbed by handling.
Thefe larva are generally to be found in {hallow Handing
waters, about the beginning of June, fooner or later as the fum-
mer is more or left favorable ; in fome feafons they are to be
found in great numbers, while in others it is no eafy matter to
meet with them. They love to crawl on the plants and grals
which grows in the water, and are often to be met with in ditches,
floating on the furface o f the water by means o f their tail, the
head and. thorax at the fame time hanging down,; and in this
fituation they will turn over the clay and dirt with their fnout and
feet in fearch of food, which is generally a vifcous matter that
is common in fmall ponds and about the fides of ditches. This
worm is very harmleft, contrary to the opinion one might form
at firft fight, from the furprizing vibratory motion of the legs,
which refembles the brandilhings o f an envenomed tongue or fling
They are moft eafily killed for diffeftion in fpirit of turpentine.
After
After a certain period they paft into the pupa form j when
they are about to change, they betake themfelves to the herbs
that float on the furface o f the water, and creep gently thereon,
till at length they lie partly on the dry furface, and partly on the
water ; when in the larva or pupa ftate, they can live in water, but
can by no means inhabit there when changed into flies : indeed;
man alfo, whilft in the uterus, lives in water, which he cannot do
afterwards. When thefe worms have found a proper fituation,
they by degrees contract themfelves, and, in a manner fcarce perceivable,
lofe all power of moving. The inward parts o f the
worm’s, tail now feparate,from the outmoft fkin, and become
greatly contrafted; this probably gives the infeft a great deal o f
pain: by this contraction, an empty fpace is left in the exterior
ikin, into which the air foon penetrates..
Thus this infeft paffes into the pupa ftate under it’s own Ikin,
entirely different from that of the caterpillar, which calls off the
exterior {kin at this time ; this change may often be obferved to
take place in the fpace of ten or twelve hours, but in what manner
it is performed we are ignorant, as it is effefted in a hidden unknown
way, inwardly within the {kin, which conceals it from our.
view.
Whilft the larva is changing under the fkin, the body, head,,
and tail, feparate infenfibly from their outward vefture. The
legs at this time, and their cartilaginous bones, are, on account
®f the parts which are withdrawn from them,, left empty; the
worm lofes alfo now the former fkull, the beak, together with
the horny bones belonging thereto, which remain in the Ikin o f
the exuvia. It is worthy of notice; that the optic nerves feparate
E e 2 . al fo