Of the frefh Water Polype. 191 
to the flrength and quantity of the nutritive juice. It 
is alfo obfervable, that they lofe their colour, if not fed 
with aliments of the fame colour to themfeVes, and like- 
wife that they will faft a great while, but then they wafte 
proportionably to their falling. 
They are alfo fubjedt to be infefled with a kind of 
aquatic lice before fpoken of, which are very common 
in expofed waters; they are of an oval figure, and gene¬ 
rally white; they run very fwift upon the polype’s body, 
and crowd about its head more than any other part, as at 
fig. 385. Nevertheless they may be feen in great num¬ 
bers running over the body ab, and arms acc. The 
prefent figure is a reprefentation of the polype and lice, 
as they appear in the microfcope. If proper care is not 
taken to keep them clean from thefe animals, they will 
be devoured by them, their arms will gradually diminifh, 
and at laft their body, till there is nothing left. Fig. 
386. reprefents one that had all its head part eat up, 
which after having been cleanfed, had a new head, and 
new arms, and became a very fine polype. 
Therefore the beft way to preferve thefe animals in 
health, is often to change the water, and that efpecially 
after they have done eating. It is not enough to pour 
it off, but they mull all be taken out, and the bottom 
and fides of the veffel rubbed clean from the ilimy fedi- 
ment adhering thereto, which is caufed by the faeces they 
difgorgc therein, which are converted into a kind of 
Ilime, fatal to them if not clear’d aw r ay. My way is to 
loofen their tails from the fides or bottom of the glafs, 
then I take them up one by one with a quill, cut fcoop 
fafhion, and place them in another glafs with clean 
water; fometimes they cling to the quill in fuch a man¬ 
ner, as not eafily to be difengaged. The only way then 
is to let the quill remain a minute or two in the water, 
till 
