55^ M i c r o s c o p i c a l E s s a y s .
It is an oval, pellucid membrane, fomething larger than the
mona lens. The fore-edge thick and truncated, the hinder-part
acute, or terminating in a fliort tail. It whirls about in various
direflions with great velocity.
143. Cercaria Difcus.
Cercaria orbicularis, cauda curvata. A fma'II orbicular cercaria,
with a bent tail.
144. Cercaria Orbis.
Cercaria orbicularis, feta caudali duplici Iongiffima. Orbicular
cercaria, with a tail, confifting o f two very long briftles.
145. Cercaria Luna.
Cercaria orbicularis, cauda lineari duplici brevi. Orbicular
cercaria, with two Ihort fpines for a ta il; the fore-part hollowed,
fo as to form a kind o f crefcent.
XII, L e u c o p H r A .
Vermis inconfpicuus, pellucidus, undique ciliatus. An invifible
worm, pellucid and every where ciliated.
146, Leucophra Confliflor.
Leucophra fphaerica, fubopaca, interaneis mobilibus; Spherical
opake leucophra, with moveable inteftines.
This animalculum, or rather aheap of animalcula, is perfectly
fpherical, and larger than moll fpecies of the vorticella ; it is femr-
tranfparent, of a yellow colour, the edges o f a dark colour. It
is filled with a number of the moft minute molecules, it rolls at
intervals from right to left, but feldom removes from the fpot
where it is firft found.
The innumerable molecules circumfcribed within this fphere
are in continual motion, and, as it were, in vehement confliff,
without any order. . From the great concourfe of combatants on
one fide, or the other, the fphere is turned either to the right
or left, the molecules going in the fame direction ; it is then tranquil
for a Ihort time, but foon the conflift becomes more violent,
and the fphere is moved towards the other fide, and continues to
move in a fpiral line. When the water begins to fail, they afiume
an oblong, oval, or a cylindric figure ; the hind-part of fome is
compreffed into a triangular fhape, and the tranfparent part ef-
caping as it were from the inteftines, which continue to-move
with the fame violence till the water fails, when the molecules
are fpread into an uninformed mafs. But this alfo foon vanilhes,
when they (hoot into the form of the cryftals o f fal ammoniac,
as defcribed by Baker, p. 3, No. 3.