the rotifera

studded with what appear to be bright yellow oil-globules. It is divided by an invagination
at its lower third into an upper portion, the true stomach, and a lower
which may be considered to be a short intestine (fig. 1, i). This lower portion frequently
lies transversely to the longer axis of the stomach. Both are thickly ciliated on the
inner surface, but the cilia of the intestine are larger, and more readily seen.
When a portion of digested food has been transferred from the stomach to the intestine,
it is kept slowly revolving by the cilia, till it is suddenly expelled through the cloaca
(fig. 1, cl). The intestine is connected with the cloaca by a short and very dilatable tube
or rectum (fig. 1, r), and ends (as has been already said) on the dorsal surface, in the
median line, just at the commencement of the foot. The rectum also is ciliated, so
that the whole of the alimentary tract from the top of the buccal funnel down to the
cloaca, with the exception perhaps of the passage through the mastax, is lined with
cilia.
The Vascular
System.
At the right of the intestine (viewed dorsally), and just under the line of the lorica's
greatest width, lies the contractile vesicle (fig. 1, cv). This is a delicate bladder which
alternately dilates and contracts, and with some regularity.
The contraction is produced by fine muscular threads, which ramify in its walls,
and cause it to empty its contents through a duct into the cloaca. Its distension is
most probably due to the fluid poured into it by two looped and twisted tubes (fig. 1, Ic),
which may be seen passing to it, one on each side of the body down from the head.
This is, however, a much disputed question, which will be discussed fully in another
place, along with the probable function of the whole apparatus.
The tubes appear to be surrounded with a granular floccose material, which here and
there dilates into irregular masses. Attached to the tubes on each side, at tolerably
regular inter\als, are five little tag-like bodies (fig. 1, vt), in which a flickering motion
may be constantly seen, sometimes presenting the appearance of a waving cilium.
There is much difference of opinion about the true structure of these tags—the
vibratile tags, as they are termed—but it is probable that their office is to direct the
perivisceral fluid into the tubes, and along them into the contractile vesicle, whence
it is driven at intervals through the cloaca.
The Muscles.
The dorsal muscles are shown in fig. 3, and the ventral in fig. 4. From the posterior
dorsal surface of the head, on each side of the cephalic ganglion, and close to it, a stout
muscle (fig. 3, l, l) slopes backward towards the dorsal surface, and is attached by a
broad base to the lining membrane of the lorica. Outside this pair is a second (fig. 3,
2, 2), similarly attached, and running rather obliquely underneath the first pair, but not
quite so stout. A similar pair (fig. 4, 4, 4) is attached to the posterior ventral surface
of the head, and to the lining of the ventral surface of the lorica. The united action of
these three pairs of muscles withdraws the head into the lorica.
When it is so withdrawn, a pair of diverging muscular threads (not given in the
figure) can be seen fixed to the lorica, just below its central notch, with their other
ends fastened to the head. These evidently oppose the action of the three other pairs
(figs. 3, l, i, 2, 2 ; 4, 4, 4) and help to draw out the head again. They are assisted in
this by a further pair of muscles (also omitted from figs. 3 and 4), each of which
is fastened at one end to the base of one of the outermost anterior spines, and
at the other to a side lobe of the head.
But the principal part in driving out both the head and the foot is borne by transverse
muscles, which are attached to the lorica at the side, and are closely applied throughout
their length to the soft organs of the body. Their sudden contraction compresses
the perivisceral fluid, and so forces out the retracted head or foot. Nothing could be
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