the rotifera

Tlie head is shaped somewhat like a truncated cone, with the larger end forward;
posteriorly it is studded with several small rounded lobes ; while from its anterior surface
rise three fleshy protuberances, crowned with stout vibrating hairs called styles.
Each side of the front of the head, or coronais rounded into a nearly circular lobe,
and along the rim of each lobe runs an unbroken row of smaller vibrating hairs, called
cilia, which are continued so as to meet each other on the dorsal surface. It is by
means of this apparatus that Brachionus both swims and procures its food.
As the head is seldom withdrawn into the lorica for more than a moment or two,
and as the cilia begin to play the instant it is protruded, Brachionus would have been
condemned to almost perpetual motion if it had not been for the foot. This organ is
provided at its extremity with two pincer-like processes, or toes (fig. 1, t); which, however,
do not pinch, but which can adhere even to glass by means of a viscid secretion that flows
through their tips.
The foot-glands (fig. 1, fg), which secrete this substance, are two club-shaped
organs running down the whole length of the foot. They are to be met with in nearly
all the Eotifera.
The cilia, which are set closely round the edge of the corona, lash the water
with such fury that it is impossible usually to follow the action of any individual cilium;
but, by selecting an animal whose corona is close to the covering glass of the live
box, some spot can often be found where the action of the cilia is checked by their striking
against the glass; and, under these circumstances, it is easy to understand their action.
Each cilium lashes sharply downwards (like a whip) on the corona, and then rises gradually
into its place again, to repeat the action continuously, so long as the corona is expanded.
As, however, the cilia do not do this simultaneously, but in turn, one after the other, in
very rapid succession, those that can be seen together at any given moment are in every
phase, from complete extension to complete depression; thus giving rise to various wavelike
illusory appearances, according to the illumination, and also to the plane on which
the objective is brought to focus. One of the most common of these appearances is that
of a toothed wheel, which is so well imitated by the Philodinadce, that early observers
thought such wheels existed, and drew them like the escapement-wheel of a watch. 2
If a little carmine be mixed with the water, two beautiful coloured spirals will be
produced by the action of the ciliary wreaths, one on each side of the head leading down
to the buccal funnel. The orifice of the buccal funnel, or, as it will be termed, the buccal
orifice, lies in a niche on the ventral surface; it is fringed by the ciliary wreath, which
here dips down on either side of the corona, and passes round the V-shaped opening of
the buccal funnel (fig. 2, bf)—that is, of the passage leading from the niche to the mastax.
The atoms brought by the ciliary currents pass down the buccal funnel, which itself is
lined with cilia ; and, if uninterrupted, enter the mastax (figs. 1, 2, mx), a muscular bulb
containing the trophi (fig. 1, ti) or teeth. But it is not every atom whirled down the buccal
funnel that is suffered to reach the mastax ; for there are two lip-like processes (fig. 2, Ip)
rising from the mastax, which can be seen every now and then thrust up and down the
buccal funnel; and which by closing prevent the passage of morsels that are not to
the Rotiferon's taste. The sudden check, produced by the lips on the inflowing current,
always sweeps out of the buccal funnel whatever the animal desires to reject; and a
constant stream of rejected particles may be seen issuing from the buccal funnel midway
between the spirals caused by the corona.
The
Mastax.
The mastax (figs. 1, 2, mx\ fig. 6) is the muscular covering of the jaws or trophi.
It has thick walls, and is slightly three-lobed, each lobe investing one of the three principal
parts of which the trophi consist. There is an opening in front towards the ventral
surface at the bottom of the buccal funnel, whose walls here merge into those of
1 A name suggested by Mr. Cubitt in lieu of trochal disk.
2 Baker on the Microscope, vol. i. Plate VIII. fig. 6, 1785.
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