MARCH.
Paramecia--Effects of Sunlight--Pterodina patina--Curious
tail--Use of a Compressorium--Internal structure of
Pterodina--Metopidia--Trichodina
pediculus--Cothurnia--Salpina--Its three-sided box--Protrusion
of its gizzard mouth.
The _Paramecia_, noticed in the last chapter, have increased and
multiplied their kind without any fear lest the due adjustment between
population and food should fail to be preserved. A small drop of the
scum from the surface of the water in their bottle is an astounding
sight. They move hither and thither in countless numbers, seldom
jostling, although thick as herrings in a tub, and in many portions of
the field the process of self-fissure, or multiplication by division, is
going on without any symptoms of discomfort on the part of the parent
creature. This is an interesting sight, but we will not linger over it,
for the sun is shining, and there is enough warmth in the air to make it
probable that the ponds will be more prolific than in the cold winter
months. Sunshine is a great thing for the microscopic hunter; it brings
swarms of creatures to the surface, and the Rotifers are especially fond
of its genial beams. Even if we imitate it by a bright lamp, we shall
attract crowds of live dancing specks to the illuminated side of a
bottle, and may thus easily effect their capture by the dipping-tube.
[Illustration: Pterodina patina.]
This year the March sunshine was not lost, for on the third of that
month I obtained a bottleful of conferva from a pond about a mile from
my house, and lying at the foot of the Highgate hills. Water-fleas were
immediately discovered in abundance, together with some minute worms,
and a ferocious-looking larva covered with scales; but what attracted
most attention was a Rotifer, like a transparent animated soup-plate,
from near the middle of which depended a tail, which swayed from side to
side, as the creature swam along. The head exhibited two little red
eyes; two tufts of cilia rowed the living disk through the water, and
the gizzard worked with a rapid snapping motion, that left no doubt the
ciliary whirlpools had brought home no slender stores of invisible food.
Sometimes the end of the tail acted as a sucker, and fixed the animal
tightly to the glass, when the wheels were protruded, and the body
swayed to and fro. Then the sucker action ceased, and as the creature
swam away, a tuft of cilia was thrust out from the extremity of the
tail. A power of one hundred linear was sufficient to enable the general
nature of this beautiful object to be observed, but to bring out the
details, much greater amplification was required, and this would be
useless if the little fidget could not be kept still.
[Illustration: Pterodina patina--gizzard.]
The size of the creature, whose name we may as well mention was
_Pterodina patina_, rendered this practicable, but required some care.
The longest diameter of the body, which was not quite round, was about
1--120", so that it was visible to the naked eye, and as a good many
were swimming together, one could be captured without much difficulty,
and transferred with a very small drop of water to the live-box. Then
the cover had to be put on so as to squeeze the animal just enough to
keep it still without doing it any damage, or completely stopping its
motions. This was a troublesome task, and often a little overpressure
prevented its success.
Some observers always use in these cases an instrument called a
_compressorium_, by which the amount of pressure is regulated by a lever
or a fine screw; but whether the student possess one or not, he should
learn to accomplish the same result by dexterously manipulating a
well-made live-box. We will suppose the _Pterodina_ successfully caged,
and a power of about one hundred and fifty linear brought to bear upon
her, for our specimen is of the "female persuasion." This will suffice
to demonstrate the disposition and relation of the several parts, after
which one of from four hundred to five hundred linear may be used with
great advantage, though in this case the illumination must be carefully
adjusted, and its intensity and obliquity frequently changed, until the
best effect is obtained.
We find, on thus viewing the Pterodina, that it is a complex, highly
organized creature, having its body protected by a _carapace_, like the
shell of a tortoise, but as flexible as a sheet of white gelatine paper,
which it resembles in appearance. Round the margin of this carapace are
a number of little bosses or dots, which vary in different individuals.
The cilia are not disposed, as at first appeared, in two separate and
distinct disks, but are continuous, as in the annexed sketch. Down each
side are two long muscular bands, distinctly _striated_, and when they
contract, the ciliary apparatus is drawn in. As this contraction takes
place, two apparently elastic bands, to which the ciliary lobes are
attached, are bent downwards, till they look like the C springs behind a
gentleman's carriage; and they regain their former position of slight
curvature, when the cilia are again thrust out.
[Illustration: Pterodina patina--tail-foot.]
The gizzard is three-lobed, and curiously grasped by forked expansions
of the handles of the hammers. The tail, or tail-foot, can be withdrawn
or thrust out at the will of the creature; and when in a good position
for observation, a slight additional pressure will keep it so for
examination. Delicate muscular longitudinal bands, forked towards the
end of their course, supply the means of performing some of its motions,
and one, or perhaps two, spiral threads extend through the upper half of
its length, and either act as muscles, or as elastic springs for its
extension. The intestines and other viscera are clearly exhibited, and a
strong ciliary action conducts the food to the gizzard-mouth.
To return to the tail. One spiral fibre is easily discovered; but I
have often, and at an interval of months, seen the appearance of two,
and am in some doubt whether this was a deception, arising from the
compression employed, or was a genuine indication.
[Illustration: A. Metopidia acuminata, as drawn by Mr. Gosse. B.
Specimen as seen and described in text. _c._ Mouth or gizzard.]
Where this Rotifer occurs I have usually found it plentiful, but
unfortunately could obtain no constant supplies after I had determined
to make a special study of the remarkable tail, which is much more
complicated than I have described. The _Pterodina_ lived for some time
in captivity, and for a week or two I could obtain them from my glass
tank. They were likewise to be found for some weeks in the same part of
the pond, but not all over it, until one day not a single specimen could
be discovered, notwithstanding a persevering search nor was I
afterwards able to get any from that pond during the remainder of the
year.
[Illustration: Trichodina pediculus.]
Several other Rotifers, with and without carapaces, were among the same
mass of confervae, among them a _Metopidia_, with a firm shell, a forked
jointed tail, and a projection in front which worked like a pickaxe
among the decaying weed. There were likewise specimens of the
long-necked animalcules (Trachelii), groups of Vorticella, some
specimens of Volvox, and a small _Trichodina pediculus_, which, when
magnified two hundred and sixty linear, was about the size of a sixpence
and equally round. The edge was beautifully fringed with a circle of
cilia; in an inner circle was a row of locomotive organs, and the centre
exhibited vacuoles constantly opening and shutting. This creature, as
before explained, is often found as a parasite upon the polyps. On one
occasion a glimpse was caught of a Rotifer similar in shape to the
common wheel animalcule, but with a yellow inside. Possibly it was the
object so beautifully delineated by Mr. Gosse, in his "Tenby," and
described as the "Yellow Philodine," but this must remain in doubt, as
it managed to escape before it could be secured.
[Illustration: A. Cothurnia imberbis--('Micrograph. Dict.') B and C. The
specimens described in text. The figures give the _linear_
magnification.]
By the 18th of the month the Vorticellids were much more plentiful, and
their changes easily watched; many left their stalks while under the
microscope, after which some rushed about like animated and demented
hats, others twirled round like tee-to-tums, while others took a rest
before commencing their wild career. But the common Vorticellae were not
the only or the most interesting representations of their charming
order, for upon some threads of conferva were descried several elegant
crystal vases standing upon short foot-stalks, and containing little
creatures that jumped up and down like "Jack in the box." These were so
minute, that a power of four hundred and thirty linear was
advantageously brought to bear upon them. When elongated their bodies
were somewhat pear-shaped, but more slender, and variegated with
vacuoles and particles of food. The mouths resembled those of
Vorticellae, and put forth circles of vibrating cilia. They were easily
alarmed, when the cilia were retracted, and down they sank to the bottom
of their vases, quickly to rise again. In one bottle there were two
living in friendly juxtaposition. This was not a case of matrimonial
felicity, nor of Siamese twins, but of _fission_, or reproduction by
division. The original inhabitant of the tube finding himself too fat,
or impelled by causes we do not understand, quietly divided himself in
two, and as the house was big enough, no enlargement was required. How
many stout puffy gentlemen must envy this process; how convenient to
have two thin lively specimens of humanity made out of one too obese for
locomotion. Man is, however, sometimes the victim of his superior
organization, and no process of "fission" can make the lusty lean.[9]
[9] Balbiani in his 'Recherches sur les Phenomenes Sexuels des
Infusoires,' speaks of the Vorticellids as the only Infusoria dividing
longitudinally. In other species such appearances arise from
conjunction.
The bottles in which these creatures live, in happy ignorance that they
are called by so crackjaw a name as _Cothurnia imberbis_, were described
as _Carapaces_ by Ehrenberg, but they bear no resemblance to the shell
of a turtle or crab. They are thrown off by the animals who preserve no
other connection with them than the attachment at the bottom.
The Micrographic Dictionary describes the family Ophrydina as
corresponding to Vorticellina with a carapace. Stein places them with
Vorticellids, &c., amongst his Peritricha, which are characterised by a
spiral wreath of cilia round the mouth.
Towards the end of the month a great number of black pear-shaped bodies
(Stentor niger), visible to the naked eye, were conspicuous in some
water from the Kentish Town ponds. Upon examination they were found to
be filled with granules that were red by reflected, and purple by
transmitted light. Each one had a spiral wreath of cilia, with a mouth
situated like those of the stentors, hereafter to be described, but none
of them became stationary, and in a few days they all disappeared. Stein
divides Ehrenberg's Stentor igneus from S. niger; the creature described
seems to have agreed with Stein's _igneus_, which he describes as having
blood-red lilac, cinnabar, or brown-red pigment particles, and as much
smaller than his S. niger. In the same water were specimens of that
singular Rotifer, the _Salpina_, about 1--150" long, and furnished with
a _lorica_, or carapace, resembling a three-sided glass box, closed
below, and slightly open along the back. At the top of this box were
four, and at the bottom three, points or horns, and the creature had one
eye and a forked tail. Keeping him company was another little Rotifer,
named after its appearance, _Monocerca rattus_, the 'One-tailed Rat.'
This little animal had green matter in its stomach, which was in
constant commotion. I ought to have observed that the Salpina repeatedly
thrust out its gizzard, and used it as an external mouth. In the annexed
sketch the Salpina is seen in a position that displays the dorsal
opening of the carapace. Its three-cornered shape is only shown by a
side view.
[Illustration: Salpina redunca.]
Here we close a brief account of what March winds brought in their
train. The next chapter will show the good fortune that attended April
showers.