xvi 
Some commence and finish their existence in the short 
space of a day, perhaps an hour, while others live 
through centuries., The same occurs among the Poly- 
pidoms ; some have only an ephemeral life, while the 
existence of others seems eternal. I here speak of the 
Polypidoms, not of the polypi ; the latter, separately 
considered, do not appear to have a long life, but on 
the contrary many circumstances induce us to pre- 
sume it is very short. 
In the Flustreas, Cellarias and Sertularias are found 
annual species, and others whose duration is sub- 
ordinate to the marine plants that support them. In 
almost all Polypidoms, the lower parts are wholly 
devoid of animalcula, and in the greater they are only 
seen at the extremities : some there are, that are en- 
tirely covered with polypi through the summer and 
autumn, but they perish with the cold of winter. No 
sooner however has the sun resumed his revivifying 
influence than new animals are developed, aud fresh 
branches are produced upon the old ones ; the lower 
part appears inert, and deprived of all kind of life ; the 
Flustreas, Sertularias, and Gorgonias afford us many 
examples. Arrived at this last stage of existence, 
the Polypidom languishes, it has no longer the power 
to resist the destructive influence of time, or the at- 
tack of those enemies which the energies of life had 
till then repulsed : some of them feed on its fleshy en~ 
