MAY.
Floscularia cornuta--Euchlanis triquetra--Melicerta ringens--its
powers as brickmaker, architect, and mason--Mode of viewing the
Melicerta--Use of glass-cell--Habits of Melicerta--Curious
Attitudes--Leave their tubes at
death--Carchesium--Epistylis--Their elegant tree forms--A
Parasitic Epistylis like the "Old Man of the Sea"--Halteria and
its Leaps--Aspidisca Lynceus.
May, the first of summer months, and of old famous for floral games,
which found their latest patrons in the chimney-sweeps of London, is a
good time for the microscopist among the ponds, for the increase of
warmth and heat favours both animal and vegetable life, and so we found
as we carried home some tops of myriophyllum, and soon discovered a
colony of tubicolor rotifers among the tiny branches. They proved to be
Floscules, generally resembling the _F. ornata_, described in a previous
page, but having a long slender proboscis hanging like a loose ringlet
down one side. The cilia or hairs were not so long as in the Beautiful
Floscules we had before obtained, nor was their manner of opening so
elegant; but they were, nevertheless, objects of great interest, and
were probably specimens of the _Floscularia cornuta_. A swimming rotifer
in a carapace somewhat fiddle-shaped, with one eye in its forehead, and
a two-pronged tail sticking out behind (the _Euchlanis triquetra_), also
served to occupy attention; but a further search among the myriophyllum
revealed more treasures of the tube-dwelling kind. These were specimens
of that highly curious Rotifer, the _Melicerta ringens_, who, not
content with dwelling, like the Floscules, in a gelatinous bottle, is at
once brickmaker, mason, and architect, and fabricates as pretty a tower
as it is easy to conceive. The creature itself stands upon a retractile
foot-stalk, and thrusts out above its battlements a large head, with
four leaf-like expansions surrounded by cilia. Between the lower lobes,
or leaves, the gizzard is seen grinding away, and above it is an organ,
not always displayed, and of which Mr. Gosse was fortunate enough to
discover the use. This eminent naturalist likens it to the circular
ventilator sometimes inserted in windows, and he found it was the
machine for making the yellow ornamental bricks of which the tower is
composed. Pellet by pellet, or brick by brick, does the Melicerta build
her house, which widens gradually from the foundation to the summit, and
every layer is placed with admirable regularity.
In order to obtain the materials for her brickmaking the Melicerta must
have the power of modifying the direction of the ciliary currents, so as
to throw a stream of small particles into the mould, which is a muscular
organ, and capable of secreting a waterproof cement, by which they are
fastened together. The result is, not to produce anything like the tubes
made by the caddis-worms out of grains of sand, but entirely to change
the appearance of the materials employed. All large particles are
rejected, and only those retained which will form a homogeneous pulp
with the viscid secretion; and when the process is complete the head of
the creature is bent down, and the pellet deposited in its appropriate
place. Each pellet appears originally to possess a more or less conical
figure, but when they are squeezed together to make a compact wall they
all tend to a hexagonal form, by which they are able to touch at all
points, and any holes or interstices are avoided.
According to Professor Williamson the young Melicerta commences her
house by secreting "a thin hyaline cylinder," and the first row of
pellets are deposited, not at the base as would be expected, but in a
ring about the middle of the tube. "At first new additions are made to
both extremities of the enlarging ring; but the jerking constrictions of
the animal at length force the caudal end of the cylinder down upon the
leaf, to which it becomes securely cemented by the same viscous
secretion as causes the little spheres to cohere."
Round the margins of the lobes or expansions may be seen delicate
threads towards which others radiate; these are thought by Mr. Gosse to
be portions of a nervous system, and two calcars or feelers serve as
organs of relation. The young Melicertas are likewise furnished with a
pair of eyes, which are probably rudimentary, and disappear as they grow
up.
The Melicerta tubes, being large enough to be visible to the naked eye,
are easily crushed in the live-box, and to avoid this, they are
conveniently viewed in a shallow glass cell, covered up as before
described. By occasionally changing the water one may be kept for days
in the same cell, and will reward the pains by frequently exposing its
flower-like head. Usually the horns or feelers come out first, and then
a lump of flesh. After this, if all seems right, the wheels appear, and
make a fine whirlpool, as may be readily seen by the use of a little
indigo or carmine.
The Melicerta is, however, an awkward object to undertake to show to our
friends, for as they knock at the door she is apt to turn sulky, and
when once in this mood it is impossible to say when her fair form will
reappear. At times the head is wagged about in all directions with
considerable vehemence, playing singular antics, and distorting her
lobes so as to exhibit a Punch and Judy profile. When these creatures
die they leave their tubes, which are often found empty in the ponds
they frequent. The Melicertas are conveniently viewed with a power of
from sixty to one hundred linear, and a colony of them may be kept alive
for some weeks in a glass jar or tank.
Among the remainder of my tiny captives were two beautiful members of
the Vorticella family, _Epistylis_ and _Carchesium_. The reader will
remember that in the Vorticella previously described, the bells stood
upon stalks that were very flexible, and retractile by means of a muscle
running down their length. The _Epistylis_ is, as its name imports, the
dweller on a _pillar_. The stem is stiff, or only slightly flexible, and
has no apparatus by which it can be drawn down. The specimen mentioned
stood like a palm-tree, and the large oval bells drooped elegantly on
all sides, as its portrait will show. At times they nodded with a rapid
jerk.
[Illustration: Epistylis.]
The _Carchesium_ differs from the common _Vorticella_, by branching like
a tree, but the stems are all retractile, although the trunk seldom
exercises the power. A group of these creatures presents a spectacle of
extraordinary beauty--it looks like a tree from fairy-land, in which
every leaf has a sentient life. In general structure the bells of the
_Epistylis_ and the _Carchesium_ resemble the common _Vorticella_, and
like them may be seen with a power of about one hundred linear for
general effect, and with a higher one for the examination of special
points. Pritchard notices three species of _Carchesium_, and eighteen of
_Epistylis_;[13] some of which it is to be hoped will turn out to be
only varieties.
[13] An interesting _Epistylis_, called _Digitalis_, from its bells
resembling fox-glove flowers in shape, occurs as a parasite upon the
_Cyclops quadricornis_, a very common entomostracan in fresh-water
ponds. At this moment I have a beautiful specimen, branching like a
bushy tree, and attached to the tail of a _Cyclops_, who can scarcely
move under his burden, which is like Sinbad's "Old Man of the Sea."
Towards the end of this month rotifers abounded, and polyps were
plentiful. Among the rotifers was one about a two-hundredth of an inch
long, protected by a carapace, and having a tail terminating in a single
style, hence called "Monostyle." There is perhaps no class of creatures
that present so many curious and unexpected forms as the rotifers; and
although we have noticed a good many, there are far more that remain to
be found and described.
The water in which the preceding animals dwelt was enlivened by the
jumps of the _Halteria_, a little globe surrounded by long fine cilia,
with which its movements were effected; and its companion was the
_Aspidisca lynceus_, an oval animalcule, having a distinct cilia or
_lorica_, and furnished, in addition to cilia, with bristles, which
enable it to walk and climb as well as swim.
There were also some eggs of rotifers attached to the water plants, in
which motion could be descried at intervals, and a little red eye
observed. These eggs are always large in proportion to the creatures
that lay them, and if they escape being devoured by enemies, may be
watched until their contents step forth.
In this, as in other months, omission is made of creatures that have
already come under notice, or our list would assume larger dimensions.