576 
THE HYDRO IE A. 
is worthy of notice, that the Gforgonise are never bushy, and, for the most part, have their 
branches in the same plane. 
In this illustration we have an example of a very interesting 
and extremely beautiful species. 
The Sea-peu is so named because its whole form bears the 
most remarkable resemblance to a quill-feather, consisting of a cen- 
tral shaft, from which a double row of “pinnae” is developed at 
right angles, bearing the polype on their upper margin. As may 
be seen by the illustration, the whole form of this curious being is 
remarkably graceful, and it really seems as if it had been modelled 
upon a quill-feather plucked from the wing of some bird. 
The Sea-pen is never attached to solid substances, but remains 
quite free in the ocean. It does not, however, swim, but is a help- 
less sort of being, and only kept in its proper position by the base 
being thrust into the mud or sand at the bottom of the sea. Some 
species of Sea-Pinnae are phosphorescent, and present a magnificent 
sight in the darkness. It was once thought that the creature was 
able to swim by means of the webs, or pinnae, which flapped like 
the fins of a fish, but it is now ascertained that no such power 
resides in these organs. The stem is of a rather soft consistency, 
strengthened by a bony centre, which reaches nearly to its tip. 
An object of somewhat similar form, but considerably elon- 
gated, and with the pinnae proportionately shorter, is called Sea- 
rush ( Virgularia miroMlis), an animal belonging to a genus 
that can easily be distinguished from the preceding by several peculiarities. The pinnae 
are short, deeply scooped above, and, with their bases, partly surround the central stem. 
The polypes are set only upon the edges of the pinnae. There is an allied species belonging to 
the same family, called by the name of E (monaria. In this remarkable genus, the general 
shape of the lengthened mass is four-sided, and the polypes are arranged in a somewhat 
spiral form on the stem, but only one side of its latter half. In temperate seas, the Sea-rushes 
do not grow to any great length ; but under a tropical sun they reach great dimensions, some 
of them measuring more than a yard in length. 
A very curious inhabitant of some seas, which is in the habit of encrusting all kinds of 
marine bodies, such as shells, stones, and stems of the large algae, is popularly known under 
the name Sea-eingee (. Alcyonium digitatum ). Its general mass runs into lobes, and is of a 
soft, spongy consistency, pierced with little holes, from which the polypes make their appear- 
ance when in health. When closely examined, the little holes or pores are seen to be formed 
of eight rays, in a kind of star-like pattern, and corresponding to the tentacles of the polypes 
which inhabit them. These little cells are placed at the ends of canals, which permeate the 
whole mass, and serve to unite into one common body the vast number of polypes which are 
thus aggregated together. When examined by the microscope, the substance of the polyp- 
idon is found to be filled with tiny particles of chalky matter, which serve to give consistency 
to the fabric, and add to its elasticity. 
SEA PEN .—Permatula grisca. (One- 
quarter natural size, b, Enlarged 
cell.) 
HYDROIDA. 
We now arrive at the order Hydroida, which are known by the internal cavity being 
simple, and the creature increasing by buds thrown out from the sides. The Tubulariadse are 
the first family of these creatures. In the Tubulariadse the buds grow from the base of the 
tentacles, and break off their attachments as soon as they have attained maturity. The buds, 
