ty i Of the frejh Water Polype. 
The third fort, for the moft part, let their arms hang 
down, making different turns and returns, as at fig. 333. 
and fometimes they diredt fome of them towards the top 
of the water. 
Their progreffive motion is performed by means of 
that faculty they have of firetching out, contracting, and 
turning themfelves every way. For let the polype a b, 
fig. 349. be fixed by its poflerior end b, having its body 
a b, and arms extended in the water, in order to ad¬ 
vance, it draws itfelf together, by bending its body on 
whatever it moves ; and then fixing its anterior end a 
upon this body, fometimes the anterior end only, at other 
times fome of its arms, and at others the arms and an¬ 
terior end a, as at fig. 350. When the anterior end is 
well fixed, it loofens the poflerior end b, and draws it 
to the anterior a, fallening the end b, as at fig. 351. 
after which it again loofens its anterior end a, and 
flretches it out, as at fig. 352. Thus much for a ge¬ 
neral defcription of the common fleps a polype makes 
In moving from place to place. 
They walk very flow, and often flop in the middle of 
a flep, difpofing of, and winding their body and arms 
every way; as at fig. 338. 
Sometimes they make an extraordinary flep, as fol¬ 
lows, let the polype a b, fig. 353. be fixed by its pofle- 
rior end b, and its body and arms extended in the water. 
Firfl it bends its anterior end a, towards the body upon 
which it moves, and fixes it at a, fig. 354. after which 
it loofens its poflerior end b, and raifes it up perpendicu¬ 
larly, as at fig. 355, then bending its body to the other 
fide, fixes the poflerior end b, as at fig. 356. and loofen- 
ing the anterior end a, raifes it up again, as at fig. 357. 
The third kind of flep the polype makes, is in the fol¬ 
lowing manner 5 let the polype a b, fig. 358. be fixed by 
its 
