ON POLYPI. 579 
them into a vessel full of water. After a certain term of re- 
pose, the hydr are observed to begin to move and agitate 
their tentacula, as in their ordinary position. Trembley, who 
thus preserved and studied them for several consecutive 
years, used to feed them with daphniz, and other small 
aquatic animals. 
The VorTICELLA of Miller, is a genus concerning which 
some controversy has existed, as to whether it should be 
placed with the polypi or the infusoria. ‘The common cha- 
racters of the animals composing it are, that they are naked, 
contractile, and provided with rotatory organs. But they 
present enormous differences, some being binary animals, ap- 
pendiculated, and very complex, others appearing radiated 
and very simple. 
The organization of the true vorticelle is much more 
simple than that of the species retrenched from them by M. 
de Lamarck. In fact, the vorticelle exactly resemble a flower 
of the lily of the valley, supported upon a long filament. 
This filament is cylindrical, and a little enlarged at its ter- 
minal part. The body itself is formed like a small purse or 
monopetalous flower, having its edges widened, and _ pro- 
vided with groups of short and very fine ciliz, opposed 
laterally, which should make the vorticellz binary animals. 
When these little beings are in their state of complete deve- 
lopment, they are attached to some submerged bodies by the 
extremity of the pedicle, this part being extremely stretched, 
as well as the body, at the anterior of which the two fasciculi 
of cilia are agitated with great rapidity. From this action 
results a sort of double vortex, or whirlpool, which separates, 
or drives out, the extremely fine molecules which are found in 
the ambient fluid, and which is regarded as serving to direct 
the prey towards the buccal cavity. On the least shock, these 
little animals contract themselves quickly, undulating their 
pedicle, which being fixed, serves them as a point of rest. 
Pp2 
