Of the Wheel Animal . 279 
moft careful Examination ; for as the Heart 
d may be feen therein more diftindtly, its 
Figure and Motions may confequently be 
oblerved much better in this than in any 
other fmall Creature I have met with. 
The Heart d is placed almoft in the Mid¬ 
dle of the Thorax, where its Syftole and 
Diaftole can’t fail to catch the Eye of every 
attentive Obferver; for it is feen through 
the Back of the Infedt very plainly, {hut¬ 
ting and opening, alternately, with great 
Regularity and Exadtnefs. Its Size is pro¬ 
portionable to the Creature’s Bignefs, and 
its Shape during the Syftole or Time of 
Contraction is nearly circular, being com- 
pofed feemingly of two femi-lunar Parts, 
which then approach each other, laterally, 
and form between them a roundifh or Horfe- 
fhoe-like Figure, whofe upper Side is flat, 
but the under one convex. The Diaftole is 
performed by a feeming Separation or Open¬ 
ing of thefe two femi-lunar Parts, where¬ 
by the tranfverfe Diameter of the Heart 
is very much enlarged. This Separation 
begins exadtly in the Middle of the lower 
Part next the Tail, and opens to luch a 
conflderable Width upwards, that the two 
Parts when at their utmoft Diftention feem 
only joined by an arched Veflel at their 
anterior End. The alternate Motions of 
Contraction and Dilatation are performed 
with great Strength and Vigour, in pretty 
T 4. much 
