64 CLASS II. 
old trees may afford an emblem of perennial youth: every spring 
they are covered again with leaves as fresh as those they had fifty 
years before. The stem alone is old, the leaves are still young 
again. nei 
We might be able, from the branching of the fresh-water Polyps 
from their living stem, to explain the plant-like forms of Corals 
and other such marine products. When a Polyp does not consist 
of a single soft mass, but contains a harder substance, or is sur- 
rounded by a calcareous sheath, then from the union of many such 
a body may arise which resists decomposition, and as such after the 
death of the Polyps, may be preserved in our collections for a 
length of time, as for ages they have been preserved im the cal- 
careous strata of our mountains, formed at the bottom of the sea in 
a former epoch of the world. his common mass is named a Poly- 
pary or Polypstock (Polyparium)}. After the Polyps had been dis- 
covered, these stone-plants, as they had been called, were supposed 
to be the work of the animals that dwelt in them, and were com- 
pared to the cells of bees. This view of the matter does not now 
require confutation. ‘That of LAmaARcK and others agrees more 
closely with the true nature of the process; they consider the 
polypary to be a secretion upon the surface of the Polyps, and com- 
pare it with the shells of Molluscs (Snail or Mussel-shell). As 
there are Snails both naked and with shells, in like manner there 
are Polyps that are naked, and that are shut up in tubes: and the 
Polypstock is the union of the shells caused by the connexion of 
the Polyps that lived in them. Thus the Polypary would be, on 
this view, a dead substance, deposited in layers like a mussel-shell. 
Though this be nearer the truth than the earlier idea according 
to which the Polyps built their houses, still it does not entirely 
accord with the true nature of the process. Observation proves 
that this part, at least in many species, has a proper life, that it is 
nourished, grows, and is the seat of that gemmation whence new 
1 It appears that REAUMUR first invented this appellation, now in common use ; 
“‘Auroit-on pu prévoir. . . . que ces corps qui sembloient avoir végété dans la mer, étotent 
pour les polypes ce que les guépiers sont pour les guépes ; quon ne devoit plus leur laisser 
le nom de plantes et que pour leur en imposer un qui exprimat exactement ce qu’ils sont, on 
devoit les appeller des polypiers?” Mém. pour servir a UV Hist. des Insectes. Tom. v1. 
Préface, p. 69. 
