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JOURNAL
OF THE
ROYAL MICROSCOPICAL SOCIETY.
FEBRUARY~81.
TRANSACTIONS OF THE SOCIETY.
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I.- On (Eci.9tes Janus and Floscularia trijolium, two new species
of Rotijers. By C. T. HUDSON, M.A., LL.D., F.R.M.S.
(Read 8th December, ~8Q:2
PLATES
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I.
AND
II.
(Ecistes Janus.
THE new tube-making rotifer, (Ecistes Janus, was discovered by
Mr. J. Hood, of Dundee, in Loch Lundie, in September of this
year (1880). It appears to prefer deep. water as its habitat, and
is found in the greatest number and best condition, Mr. Hood tells
me, at a depth varying from 6 to 10 feet. At first sight it was
naturally supposed to be a specimen of (E. pilula, which, so far as
its tube is concerned, it very closely resembles; but the unfolding of
its trochal disk at once showed Mr. Hood that he had secured a prize.
(E. Janus is a most striking addition to the Melicertidre, for it
EXPLANATION OF PLATES I.
AND
11.
(Ecistes Janus.
FIG. I.-Female in tube, antoral view, expanded.
,,2.
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out of tube, nearly oral view, expanded.
3."
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side view, expanded.
"4.,,
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"closed.
" 5.-Trochal disk; showing its thickenings.
" 6.-Extremity of chin.
" 7.-An antenna.
Floscularia trifolium.
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C.T. Hukon- <~l..
FIG. I.-Three females, from different points of view.
" 2.-Side view of the body.
" 3.-Back view of trochal disk; showing the two rows of setal down one
side of a lobe.
In all the figures :-a, horseshoe row of small cilia; b, longitudinal muscles;
c, antenna; d, crop; e, tube from mouth into crop; f, mastax: g, ovary; h,
stomach; k, its lower division; I, vent; m, transverse muscle; n, gastric gland;
0, ganglion; p, thickening of trochal disk; r, curved bristles; s, knob-covering
gland; t, ciliated chin.
Ser.2.-VoL. I.
B
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Transactions of the Society.
form,s a connecting link betw~en the two, genera rEcistes and
Melwerta; the upper half of Its trochal dIsk bl}inO' that of the
latter, while t~e lo~er half is that of the former. Seen from the
oral surface as m FIg. 2, no one would suppose it to be other than
a true Melicerta, living i~ a tube of frecal pellets; but viewed from
the. anto:al surface as m Plate I., Fig. 1, its relationship to
rEc~stes !S ~t once appar~nt, for though the upper half of the
trochal dIS~lS deeply cl.eft mto two lobes (just as in Melicerta), the
lower half IS almost a smgle lobe, there bemg the slightest possible
hint of a notch at the lowest point.
.It would. seem then, at first, as if this new species ought to
deCI~e the. pomt a:s to whether the five genera, rEcistes, Limnias,
TUbwolana, Melwerta, and Oephalosiphon should be reduced to
one, as Gosse proJ?ose~ nearly twenty years ago'; for as the
form of the trO?hal dISk IS one of the main differences between these
genera, the eXIstence of a species possessing half the trochal disk
of one ~enus and half of another, sho~s, one wo.uld say, that the
separatIOn of the ~enera cannot easIly be mamtained. Gosse
thou~ht that the differences 6~ the trochal disks, &c., were not
suffiCient to wa:rant the formatIOn of five genera of such similar
creatures, e~peCIally when, as was the case when he wrote, each
genus contamed but one species.
At the date of. Gosse's paper, the five genera were represente~ onl~ by rE~~stes c~ystallinus, Lim't}'ias ceratophylli, T1~bi­
c?lana n~~as, Melwerta 'nngens, Oephalos~phon Limnias; but the
list I!0W IS exte~ded as follows: .rEcistes .crystallinus, rE. longicorms. (H. DaVlS, 1857), rE. mtermedws (H. Davis, 1867)
rE. pdula (J. G. Tatem, 1868), rE. umbella (F. Oxley, 1~79);
rE..Janus (J..Hood, ~880); Limnias ceratophylli, L. annulatus
(BaIley); Melwerta nngens, M. tUbicolaria ( ==TUbicolaria naias
= M. Tyro); Oephalosiphon Limnias. '
The only genus with a single species now is the very wellmarked one Oephalosiphon, and Mr. Hood tells me that he has
seen a n.ew spec~e~ of this genus on the weed from Loch Lundie.
. W~ile ~mlttmg, then, the close connection of these genera I
stI~l thmk .It would b~ inexpedient to reduce them all to o~e.
WIth ~he sm~le exceptIOn of rE. Janus (and in its case only from
one pomt. of VIew), the old genera are at once recognizable by their
trochal disks, and generally by their tubes.
. The new rotifer is, ~ think, an rEcistes rather than a Melicerta.
It IS, true th~t Mr. C~bltt named Mr. Tatem's very similar rotifer
Mehcerta fdula; b~t that was because he was avowedly adopting
~r. G?sse s sugges.tIOn of reducing the five genera to one: M.
pdula IS a true rEczstes.
. No o~e who has ,watched fJ!J. Janus open its trochal disk could
mIstake It for a Melwerta. LIke rE, umbella, and indeed like all
On rEcistes Janus, &c.
By O. T. Hudson.
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members of this genus, the disk is in many places very thin and
transparent, while across it run stout thickenings, Fig. 5, between
which the thinner portions are folded when the disk is closed, and
which serve both to open the disk and to keep it extended in
various degrees-acting indeed somewhat like the ribs of an
umbrella. These stout 'ribs protrude in a squarish bundle when
the creature begins to open its disk, and give the head a most
characteristic outline, which I have drawn in the case of rE.
umbella in this Journal, vo!. ii. (1879), p. 1. The contrast
between the thinner and thicker portions of the disk is well seen
in a side view, as in Fig. 3, especially with dark field illumination,
under which the ribs, p, p, stand out distinctly, while the substance of the disk between becomes nearly invisible, its edge being
marked out by the two parallel curves of cilia.
rE. Janus is a large rotifer, and the cilia of its trochal disk are
unusually fine, while the groove that lies between the primary and
secondary rows of cilia, is both broad and deep. Should the
motion of the larger cilia be checked by contact with the side of
the cell in which it has been placed, they may be easily counted,
while their whip-like mode of action becomes plainly, visible.
Even in the case of the finer secondary row, individual cilia may
be occasionally seen, while the combined effect of the whole does
not admit of question. As in all the Melicertid83, the action of the
larger cilia draws a current of water at right angles to the trochal
disk, and atolll8 floating in the current impinge on the disk, slide
over its surface, and then slip over the edge between the bases of
the larger cilia into the groove between the two rows, along which
they are driven by the smaller cilia to the mouth. Above the
mouth the groove ends in two ciliated knobs, which are constantly
approaching to or receding from each other as they regulate the
supply; and beneath them again, but above the mastax, a pair of
lips, if I may use the term, are often seen to spring up to seize or
reject some morse!. The greater part of the current from the
groove passes beyond the mouth along a ciliated trough, ending in
what Mr. Gosse terms the" chin." In rE. Janus this" chin,"
Fig. 6, is peculiar in shape, being divided into two peaks. Below the
divided chin is a pair of thin walls, looking exactly like the supports
of a bracket-the chin being the bracket itself. The chin above,
the walls on each side, and the concave surface of the body which
they enclose, together make something very like Melicerta's ciliated
cup; but I have not been able to detect any cilia, while in rE.
pilula there is a distinct ciliated tract lying beneath the chin.
Below this cup-like spot is a knob, Figs. 2, 3, which is rather more
prominent than in some of the tube-makers, and just above I could
now and then see two or more curved bristles which are peculiar
to rE. Janus.
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Mr. Hood had' not only ~oticed them but he had the good
fortune, whic~ I by-e .not ~ad, to see h~w 'they were used, and to
watch the roMer bUIldmg hIs tube. AslS the case in all the tubem~kers, there is ~ .inner gelatinous tube generally of considerable
thICkness, and thIS IS secreted by the rotifer itself. The outer case
is formed by fre~l pellets, which are laid 'one by one in spiral
curves round the mner one; a mode of fortifyinO' the tube which
is adopted also by (E. pilula.. The pellets ad~re pretty' firmly
togethe~, and must ma~e ~ very efficient protection for the timid
and delIcate creature w~thm, for I watched an annelid doing its
best to pull a tube to pIeces, and though the worm nibbled at the
pelle.ts, and ro~ghly: pushed the tube backwards and forwards for a
cons~d~rable tIme, It seemed quite baffied by its toughness and
elastICIty, and went away at last leaving the rotifer, who was hauled
down clo~e ~t th.e bottom of the tube, unharmed within.
In ~UIldmg Its tube, Mr. Hood says that" the animal does not
approprIate ev.ery frecal. pellet as it is voided, but only one now and
then. as. occasIOn reqUIres. It generally stoops to emit a pellet,
and havmg d~ne so. allows t~e pellet to float away, but when it
means to use It for the tube, It takes an erect position and seizes
t~e ~ellet by th~ bristle~, Fi~. 3, r, above the knob, and retires
WIth It a short dIstance mto Its tube; it then stoops its head and
places the pellet on the edge of the tube, pushing it off the bristles
by the help of the knob."
. Mr. Hood also informs me that he has seen the male, and that
It much resembles ~hat of Melicerta tubieolaria. Of the young
~emale, he says that It takes four days after it is hatched to acquire
Its perfect form, and ten days to acquire its full growth. This
seems ~ slow rate of growth for so minute a creature but some of
the.rotlfers tak.e longer still; for instance, I once h;d the opportumty of watcbI?g the growth of a young Oephalosiphon Limnias,
and It took qUIte twelve days to attain to half the size of the
full-grown ammal.
Floscularia trifolium.
~r. ~ood has also discovered another striking novelty in Loch
L.undw, VIZ. a very large Floscule, having only three lobes and
of gr~t transparency and ?eauty; indeed, as its discoverer' well
says, th~ belle of the. rotlfers." At first sight I thought it
was F. trtlobata, deSCrIbed by Dr. Collins in 'Science-Gossi '
~anuary 187::l; but the differences between Dr. Collins' descr~­
tion and 1\;11'. Hood's rotifer are great.
F. trzlobata is said to have much shorter setal than other
~loscu~es have, to have its dorsal lobe generally much larger
an. t e ?ther two, and. to have a very long cloaca running up
the sld.e of the body OppOSIte to the dorsal lobe, and ending between
On (Ecistes Jantts, &c.
By O. T. Hudson.
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the two smaller lobes on the level of their basis; and although said
to be one of the" largest of the Floscules," its "total length" is
given at in of an inch.
Now F. trifolium has setal of about the usual length, its
dorsal lobe is only slightly larger than the other two, its total
length is ft of an inch, and its cloaca and vent (as in all other
Floscules I am acquainted with) are on the side of the dorsal lobe.
It is possible that tlIe two animals are the same, for there must, I
think, be at least one grave error in Dr. Collins' description, viz.
that as to the cloaca; but as I have to choose between the possible
error of describing two different rotifers under the same name, or
the same rotifer under two different names, I have thought the
best course to be to call Mr. Hood's Floscule trifolium, and give
trilobata a chance of putting in an appearance on some other
occasion.
Dr. Collins also states that P. trilobata has its setre arranged
in an unusual manner, "being placed between their lobes as well
as on their summits, forming a kind of unbroken fringe along the
entire margin of the disk"
Now in F. t1'ifolium the setre are also set along the entire
margin of the disk, but the arrangement is not novel, for it is
exactly the same in F. campanulata. The fact is that the setal in
these Floscules are so placed that it is impossible to see all those
on one lobe at once. No three of them are in the same plane.
While those on the top of the lobe point forwards from the body,
those at the bottom of the lobe actually point backwards towards
the foot, and as they pass down the margin of the lobe from
its highest to its lowest point, their inclination constantly changes
so as gradually to alter from the first of these directions to the
latter. The consequence is that, look at the lobe from what point of
view you will, many of the setre must be invisible, as they are actually
pointing right up the Microscope. Then again, although really
very long, they often look short from their curvature taking their
upper portions right out of focus. F. trifolium has, however,
a second smaller row of setre, much shorter, and running round
each lobe parallel to the larger fringe, and curved inwards. This
arrangement is shown in Plate n., Fig. 3, and is, I believe,
peculiar; at least I have never noticed it in any other Floscule.
If any small floating atom attempts to escape from the meshes of
the living net formed by the interlacingsetre, a swift wave of
motion is seen to run all along the smaller row, and it is often
caught and thrown back into the hollow globe formed by the three
lobes.
The first thing that strikes the observer on watching the furled
head protrude from its tube is the great size of the rotifer, and the
curiously shrivelled appearance that the lobes of the trochal disk
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Transactions of the Society.
have as they emerge from the opening head. In a few seconds the
lobes gently expand, the many folds and creases slowly disappear,
till at last the eye is gratified with the sight of a lovely diaphanous
tulip, the rim of which is fringed all round with delicate and
motionless hairs.
Neither pen nor pencil can do justice to the exquisite grace of
this beautiful creature. From every point of view the flowing
curves of the trochal disk are charming, and its great transparency
permits of the whole outline of the rim being seen at once. One of
the lobes (that usually termed the dorsal one) is rather larger than
the others, and it is slightly curved over the mouth; across each
lobe run delicate muscular threads for furling it. The expansion of
the lobes is doubtless produced by the transverse muscles of the
body, which, by compressing it, force fluid upwards between the
two membranes of which the lobes are composed. This can be
readily seen in F. campanulata, in which the fluid carries along
with it numbers of granules, whose rush upwards to the lobes, as
the Floscule expands, is easily visible under dark field illumination.
It was for a long time a moot point how the vortex was caused
which, setting down between the lobes, drew its prey to the
Floscule's mouth; and at last it was made out that a horseshoeshaped row of very fine cilia (Figs. 1 and 2, a) lay at the bottom of
the lobes where they join the neck. If F. trifolium had been a
common rotifer, there would have been no difficulty about the
matter, for this row of small cilia can be easily seen in almost any
position, owing to the animal's great size and transparency. It is
unnecessary to describe in detail its other organs, as so far as I
have observed they are in no respect different from those of the
other Floscules.
I will conclude, therefore, by hoping that Mr. Hood will not
leave Loch Lundie unvisited next summer, and that the skill and
perseverance which he showed when he fished up <E. Janus from
a depth of ten feet, will often be turned to good account in that
admirable hunting-ground.
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. SOC . SER..ll ·\[OI.I.Pl .. 1I
JOUHN R .MICK
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C. T.Huikon- U.