The circular bodies which projeft from them have much the
refemblance of wheels, and feem to turn round with confiderable
velocity, by which means a very rapid current of water is brought
from a great diftance to the mouth of the little creature; as thefe
wheels are very tranfparent, except the edge, which is fet with
fibrillae, (as cogs to a wheel) it is difficult to determine how they
are turned about, or what is their real figure, whether they are
flat, concave, or conical; be this as it may, they are protruded
from a couple o f tubular cafes, in which they can be again re-
trafted, at the will and pleafure o f the animal. They do not
always turn the fame-way, nor with the fame velocity; they will
fometimes move in contrary directions, fometimes both one way.
The figure varies, from the degree of their protrufion, and from
other circumftanees. They appear fometimes like minute oblong
fquares) rifing from the periphery o f .a circle; at other times they
terminate in fharp points, fometimes they are curved, bending
the fame way like fo many hooks ; now and then the ends appear
clubbed, or in appearance like a number of little mallets.
When the fore part of this creature is firft feen to open or
divide, the parts, which when fully protruded referable wheels,
feem only like a couple o f femicircles, the edges whereof, are fet
with little fpicalse, having all a nimble and continual vibrating
motion upwards and downwards, whereby the water becomes
agitated, each wheel being in this cafe doubled, or like a round
piece of paper folded in the middle.
When the wheels are in motion, the head appears very large
in proportion to the fize of the animal; and though it is then
every-where tranfparent, yet a ring or circle, more particularly
remark-
M i cros cop i ca l E ssays, 629
remarkable for it’s brightnefs, may be perceived about the middle
o f the forehead; many vefiels may be feen to take their
origin from this.
The thorax, or breaft, is joined to the head by a fhort annular
circle or neck; the thorax in fize is nearly one-fixth part o f the
whole animalculum. In it we diftinajy perceive the heart of the
little creature ; the heart is placed almpft in the middle, the diaf-
tole and fyftole cannot fail to catch the eye of every attentive
obferver. It is feen very plainly through the back, lhutting and
opening alternately with great regularity and exaftnefs. It appears
to be compofed of two femiljunar parts, wich ip the time of
coniratuon approach each other laterally, apd !t>rm between
them a figure fomewhat like a horfe-fhoe, whole upper fide ,is
flat, the under pne convex. In the diaftole. thefe two parts
feparate; the feparation begins exactly in the middle o f the lower
part next the tail. The .alternate motions of the heart are performed
with great ftrength and vigour. In each ,of the femilunar
parts there is a cavity, which doles when they come together,
and opens when they feparate.
The motion of the heart is communicated to all the other parts
of the thorax, and indeed through the whole animal we may perceive
contrafiions and dilatations going on, that are apparently
correfpondent thereto. It is neceffary, however, to remark,
that themotion of the heart is fometimes fufpended, or at leal!
quite imperceptible for two or three minutes, after which it recommences,
and goes on with the fame vigour and regularity as
before. From1-!16 under part o f the thorax a finall tranfparent
e horn