460 POLYPI, 
hollow ovoid, open at both ends and with two envelopes, both per- 
forated by meshes like the Retepora*. 
In the fourth tribe the animal rind or bark encloses a mere fleshy 
substance without an axis either osseous or horny. In 
Atcyonium, Lin., 
As in the. Pennatule, we observe Polypi with eight denticulated 
arms, and intestines prolonged into the common mass of the ovaries: 
but this mass is not supported by an osseous axis; it is always fixed 
to the body; and where it is drawn out into trunks and branches, 
nothing is found internally, but a gelatinous substance traversed 
by numerous canals surrounded with fibrous membranes. The bark 
is harder and excavated by cells, into which the Polypi withdraw 
more or less entirely. The 
A, digitatum, Ell., Corall., XXXII, which is divided into thick 
and short branches; and Tes A, exos, Where branches are more 
slender, of a heatiatul red, &c., are very abundant in European 
seas. 
Linneus and his successors have rather lightly united to the Al- 
cyonia various marine bodies of different tissues but always without 
any visible Polypi. Such are 
Tuertuya, Lam., 
Where we observe the interior roughened with long, siliceous, spiral 
lines, which unite on a similarly siliceous and central nucleus. The 
crust, as in Spongia, presents two sorts of holes; the first, closed by 
a sort of grating, must be for the intermission of water, and the second, 
which are gaping, for its exit f. 
After the Alcyonia are also placed the 
Sponeia, Lin. +, 
Or Sponges; marine, fibrous bodies whose only sensible portion ap- 
pears to be asort of tenuous gelatine, which dries off, scarcely leaving 
a trace of it, and in which neither Polypi nor other moving parts 
have yet been discovered. Living Sponges are said to exhibit a sort 
of tremulousness or contraction when they are touched; it is also 
affirmed that the pores, with their superficies, are perforated, and 
* The Réféporite, Bosc., Journ. de Phys., June 1826, For these genera of little 
free Millepora, see also the work of Lamouroux just quoted. 
+ See Messrs. Audouin and Milne Edwards, Ann. des Sc. Nat., XV, p. 17. 
N.B. A great portion of the Alcyonia of Lam. belong in reality to his Thethyee. 
Add the fossil genera, which M. Lamouroux thinks be can approximate to the 
Alcyonia or Thethye: his HALLIROE, and those which form his order of the Ac- 
TINIARIA; his CHENONDOPORA, HIPPALIN2, LIMNORE®, SEREX, &c.—all pro- 
ductions of which the nature is more or less problematical. 
t The genus of the Sponges is extremely rich in curious species, and would well 
repay its study. M. de Lamarck—An. sans Vert., II, 345, et seq-—will prove an 
excellent guide. See also the important Memoir of M. Grant, Ann, des Se. Nat., 
XI, pl. xvi, 
