Hyduoiua. KADIATA Astkkoiija. 399 
of vesicular granules held togetlier by a semi-transparent, 
glairy gelatine. They are very contractile, and can 
change their form at pleasure. The tentacula sur- 
rounding the mouth are generally numerous, and are 
always simple and filiform, or tapering a little towards 
the extremity, and have their surface roughened more 
or less with granules arranged in an imperfectly verti- 
cillate fashion. These granules are possessed of a 
peculiar apparatus adapted for paralyzing and killing 
the animalcules the Polype feeds upon. They are 
similar in form and function to what in the Acaleplm 
are called the nettling organs. In the centre of these 
tentacula is placed the month, which is very dilatable, 
and leads by a short passage into the stomach. 
The Anthozoa are propagated b}' buds or gemmules, 
and by eggs ; the former extending their individual 
life, and the latter multiplying and continuing the 
species. The bud is a shoot from the body, and is 
identical in structure with the part of the parent whence 
it pullulates. The eggs are of several kinds. One sort 
produces young, which, when first born, are very unlike 
their parents, and resemble minute Medusae. They 
are free and unattached, swimming at large in the 
water, and possess a higher organization than the adult 
animal. They have senses to guide, and muscles to 
move the body to and fro ; and it is not until they have 
undergone a series of changes or metamorphoses, that 
they become staid, their muscles and nerves disappear, 
and they fall down into an inferior order. Another 
sort produces young which undergo no change in their 
development amounting to a metamorphosis. As soon 
as they are extruded from the ovisac they settle, root, 
and glide insensibly into the resemblance of the parent 
species. A third set are in the form of ciliated animal- 
cules, which have freedom of motion, and swim in the 
water as if guided by volition and sense, whirling on 
their axis, and stopping occasionally as if in search of 
a situation on which to fix themselves. After a short 
life of this sort they obtain a proper site for their per- 
manent stay and future growth, and begin to shoot up 
into those beautiful forms peculiar to the species. 
Many, if not all of the marine Hydroid polyps, are lumi- 
nous in the dark. 
The Hydroid anthozoa are composed of numerous 
species, arranged in several families. 
The family Tubulariidce, the species of which have 
a distinct polypidom, is represented in our plate of 
Zoophytes, fig. 5, by the exotic species Tuhularia 
chjtoidea. 
The family Sertidariidce, in which the polypidom is 
plant-like, horny, variously branched, and tubiilar, is 
represented in our Plate 2, fig. 2, by the British species 
Seriularia (Dynamena) pumila, the Sea-oak coralline 
of Ellis, and fig. 14 by the exotic species Flumidaria 
secundaria. 
In the family Campanulariidce, the polypidom is 
also plant-like and horny, as in the preceding family. 
It is illustrated in Plate 2, fig. 1, by the “ Sea-thread 
coralline” of Ellis, Laomedia dichotoma, a species found 
in various parts of Great Britain and Ireland. 
The family Hpdroidce, containing the fresh-water 
polypes, so well and popularly known under the name 
of Hydra, though placed amongst the Anthozoa by | 
most naturalists, is considered by some others as equi- 
valent to an order by themselves. 
In the animals belonging to tin's family, and which 
consists of a single genus {Hydra), the Polypes are 
locomotive, single, naked, gelatinous, sub-cylindrical, 
but very contractile and mutable in form, the mouth 
encircled with a single series of granulous filiform ten- 
tacula. The Hydrse are all natives of fresh water alone. 
Though usually found attached, they can nevertheless 
move from place to place, either by gliding with imper- 
ceptible slowness on the base, or by stretching out the 
body and tentacula to the utmost, fixing the latter and 
then contracting the body towards the point of fixture, 
loosening at the same time its hold with the base. Their 
usual motion is very slow; but when seizing their prey, 
they are nimble and active. They are exceedingly 
voracious, and their long tentacula are spread out 
in all directions to entrap their victims. Worms and 
other annelids are killed almost immediately they aie 
seized, though Entomostracous crustaceans, which are 
provided with a shell, fiequently escape from their 
grasp unharmed. This has lately been explained by 
the investigations into the nettling organs which are 
found in these tentacula, and which have been already 
mentioned in treating of the Acalcphce. 
Order II.— ANTHOZOA ASTEROIDA {Asteroid 
Polypes). 
The Asteroid polypes have the polypidom variable in 
form, either free or attached, of a fleshy consistence, 
strengthened with a horny or calcareous axis, enveloped 
in a gelatinous crust in which the Pol^’pes are immersed. 
These are compound, living in societies closely united 
in a single mass by their outer skin ; and the mouth 
is surrounded with only eight fringed tentacula. The 
stomach ends in six or eight elongated processes, which 
are considered as the oviducts. The polype mass is 
ju'opagated by gemmation ; and as each species emits 
its buds in a peculiar form, the shape and size of the 
mass depends upon the manner or preordained fashion 
in which the buds are evolved. The species, again, 
are propagated or increased by eggs. These are expelled 
from the ovisacs into the stomach, and from thence 
ejected into the sea. They are ciliated, and possess 
motion, as if apparently actuated by volition. Some of 
the species are phosphorescent. By far the greater 
number have a thick, spongy outer skin, which is often 
strengthened by having variously-shaped calcareous 
grains or rugose, and more or less fusiform calcareous 
spicula, imbedded in its surface. In general the com- 
mon mass has an expanded base, by which it is attached 
to some marine body, and when the mass assumes an 
erect or branched tree-like form, the animals secrete in 
the centre of their body a more or less rigid support, 
which has been called tbeir axis, and which has some- 
times, though erroneously (from its being commonly 
seen in collections without the remains of the investing 
animal), been considered the entire coral. This axis 
is thickened by depositions of fresh layers of horny 
matter on its surface, as the mass increases in size and 
requires more support ; the increase of the thickness 
and length of the axis being always simultaneous with 
