MOLLUSCA. 53 
Orprer 1. Bryozoa. This name was imposed by Ehrenberg, who was 
one of the first to demonstrate the true nature of them. They are small 
animals, aggregated in great numbers, like coralligenous zoophytes, having 
a distinet stomach and an intestine curved upon itself, with an outlet near 
the mouth. An analogy with the Cephalopoda is apparerit in the tentacles 
which surround the mouth, and which are covered with vibrille. These 
vibrillze cause currents of water which bring the animalcula within reach, 
which serve as food. The tube into which the animal withdraws varies in 
texture, being membranous, horny, fibro-gelatinous, or calcareous. This 
tube corresponds to the outer tunic of the Tunicata, in being in organic 
connexion with the interior parts, even the calcareous matter of the harder 
kinds being deposited throughout the membranous tissues. Each tube is in 
contact with its neighbors, sometimes to the number of many thousands. 
Dr. Farre thus describes the tube or cell in the Vesicularide: ‘The 
transparent horny cell which closely embraces the body of the animal, is 
nearly unyielding in its lower two thirds, but terminates above by a flexible 
portion, which serves to protect the upper part of the body when the whole 
is expanded, in which state it is of the same diameter as the rest of the cell, 
but, when the animal retracts, is folded up, and drawn in after it, and 
completely closes the mouth of the cell. The flexible part consists of two 
portions, the lower half being a simple continuation of the rest of the cell, 
the upper consisting of a row of delicate bristle-shaped processes or sete, 
which are arranged parallel with each other around the top of the cell, and 
are prevented separating beyond a certain distance by a membrane of 
excessive tenuity, which surrounds and connects the whole. This mode of 
termination of the cell is one of constant occurrence, as will be described 
in other species, and is evidently a provision for allowing of the freest 
possible motion of the upper part of the body in its expanded state, to which 
it affords at the same time support and protection.”—PAil. Trans., 18387, 
p- 398. 
Johnston thus describes the habits of some of these animals: ‘“ Let 
us now suppose that the polypes are in a state of extrusion, and fully 
expanded, all the cilia in play, and the water whirling in rapid streams up — 
and down the opposite sides of the tentacula, carrying with them nutriment 
and the breath of life. All is quietness and security around, and the little 
creatures are evidently in a state of happiness and enjoyment; no one who 
has witnessed the microscope scene (the myriads of the little flosculous 
heads that pullulate and blossom over the entire polypidom, as thickly 
peopled as the swarming hive) can have any doubt of this, especially when 
he remarks the acuteness and vivacities of their sensibilities and actions ; for, 
under his eye, one will ever and anon suddenly sink out of view, hide itself 
within the cell, again on a sudden emerge and expand, or, it may be, lay 
itself down in repose and concealment, until digestion has freed it from a 
state of repletion, or forgetfulness has removed the alarm of an enemy. 
These positions are assumed with such rapidity, that the eye cannot trace 
the steps of the process, and large glasses and minute skill are required to 
reveal to us its mechanism.”—Lrit. Zooph., p. 241. 
ICONOGRAPHIC ENCYCLOP&DIA.—VOL. I, 17 257 
