t42 ANIMALS KILLED TV. 
have often endeavoured to difcover whether they : 
{wim by undulation of the body, or by vibrations 
of the fibrilli, which, befides producing the vor- 
tices, may raife and conduc the wheel animal by 
their aétion againft the water. But it has not 
been in my power to elucidate the fact fatisfac- 
torily ; however, I fhould incline to think they 
{wim by means of the vibrating fibrilli, fince they 
generally ceafe when thefe are drawn within the 
body (1). 
I have already fpoke of a little circle fituated 
towards the head, which appears like the junc- 
tion of two C’s by the extremities. This part is 
in conftant motion by alternate contraction and 
dilation, while the animal forms the vortex, and 
the fibrils are extended. Both Leeuwenhoeck 
and Baker have obferved it, and thought it the 
wheel animal’s heart. Are we fure it is this or- 
gan? The fituation, figure, contraction, and dila- 
tion, concur, according to the Englifh naturalift, 
to fupport the opinion. But if it is a heart, it is 
a 
(1) Some animalcula certainly may {wim in this way ; 
but the wheels of this animal in particular, bear fo {mall 
a proportion to the fize of the body, that it is difficult to 
conceive their power to convey it along ; befides, ith f{pe- 
cific gravity is greater than that of water. I fhould ima- 
gine it more probable that the wheel animal fwims by uns 
dulation—-T’. m 
