AUGUST.
Mud coloured by worms--Their retreat at alarm--A country
duck-pond--Contents of its scum--Cryptomonads--Their means of
locomotion--A Triarthra (three-limbed Rotifer)--The Brachion or
Pitcher Rotifer--Its striking form--Enormous gizzard--Ciliary
motion inside this creature--Large eye and brain--Powerful
tail--Its functions--Eggs.
In the beginning of this month a pond in the Finchley Road, a little
beyond the Highgate Archway, supplied some more specimens of the
_Pterodina patina_, described in a previous chapter; but towards the
middle of the month a visit to Chipstead, in Surrey, enabled a new
region to be explored.
It is always a treat to a Londoner to get down to any of the picturesque
parts of Surrey; the trees exhibit a richness of foliage and variety of
colour not seen within the regions of metropolitan smoke; the distance
glows with the rich purples so much admired in the pictures of Linnel,
and the sunsets light up earth and sky with the golden tints he is so
well able to reproduce. Probably the warmth of the soil, and the purity
of the air, may make Surrey ponds prolific in microscopic life; but of
this we do not know enough to make a fair comparison, although our own
dips into them were tolerably lucky.
Walking one day down a lane leading towards Reigate, where the trees
arched overhead, ferns grew plentifully in the sandy banks, and the
sunlight flitted through the branches, and chequered the path, we came
to a shallow pond, or great puddle, which crossed the way, and near the
edge of the water the eye was struck with patches of crimson colour. On
attempting to take up a portion of one of these patches the whole
disappeared, although when the disturbance ceased the rich colour again
clothed the dingy mud. The appearance was caused by thousands of little
worms, belonging to the genus _Tubifex_, not uncommon in such
situations, who thrust themselves out to enjoy the light and air, and
retreat the moment an alarm is given. Probably both actions belong to
the class described in the last chapter, as "reflex;" but it would be
interesting to know whether creatures so humble have any sense of fear.
These worms will repay observation, but in these pages we eschew all
their tribe--unless the rotifers be assigned to them--and take ourselves
once more to our especial subjects.
[Illustration: Cryptomonad--Euglena.]
Knowing that farm-ponds are usually well stocked with microscopic game,
we made a dip into one more especially assigned to ducks, and obtained
wondrous little for our pains. We were not, however, discouraged, but
made an examination of the circumstances, which determined a particular
course of action. Our piece of water was simply a dirty duck-pond, in
which no large plants were growing, and which did not even exhibit the
little disks of duckweed that are common to such situations. There was,
however, on the surface, in parts, an exceedingly fine scum of pale
yellow green, and this, armed with a teaspoon, we proceeded to attack.
By careful skimming, a small bottle was half-filled with minute organic
particles, which were likely to be interesting in themselves, and pretty
sure to be the food for something else. A small drop was placed on a
tablet of the live-box, flattened out by the application of the cover,
and viewed with a power of two hundred linear, which disclosed swarms of
brilliant green globes, amongst which were a good sprinkle of minute
creatures, like the _Euglenae_ already described, and whose little red
eyes contrasted vividly with the prevailing emerald hue.
[Illustration: Cryptomonad.]
One of the higher infusoria, whose species I could not identify, was
devouring them like a porpoise among sprats. It did not, however,
exhibit any sense in its hungry career; it moved about in all
directions, gulping down what came in its way, but often permitting the
escape of the little green things that were almost in its mouth. The
little globes rolled and whirled about without the faintest indication
of a purpose, and without exhibiting any instrument with which their
locomotion was effected. To find out how this was done, a higher power
was used, and from their extreme minuteness an amplification of seven
hundred and twenty linear was conveniently employed, although a lower
one (three or four hundred) disclosed the secret by showing that a
little whip was flourished about through the neck, which the lower power
revealed. When highly magnified, each little globe was seen to consist
of an outer case of a reddish orange colour, which was noticeable on
looking at the edges, although in the centre it was transparent enough
to show the brilliant green contents, that resembled the chlorophyll, or
green colouring matter of plants. From a short neck proceeded the
whip-like filament, which was lashed and twisted about in all
directions. These little creatures belong to the monad family, but
whether they are to be called _Trachelomonads_, or by some other hard
name, the learned must decide.
The 'Micrographic Dictionary' puts a note of interrogation to the
assertion of some writers that _Trachelomonads_ have no necks, and draws
some with such an appendage.
Pritchard's last edition is against necks, and whether the necks or no
necks are to win, is a mighty question equal at least to the famous
controversy, which divided the world into "big and little endians in the
matter of breaking eggs."
A discussion of more importance is, whether these _Cryptomonads_--that
name will do whatever comes of the neck controversy--are animals or
vegetables. Lachmann and Mr. Carter affirm that they have detected a
contractile vesicle, which would assimulate them to the animal series,
but their general behaviour is vegetable; and the 'Micrographic
Dictionary' is in favour of referring them to the _Algae_--that great
family of simple plants, of which the sea-weeds are the most important
representatives.
[Illustration: Triarthra.]
When any of the monads swarm, there are sure to be plenty of other
creatures to eat them up, and in this instance the predaceous
animalcule, already described, was not the only enemy the little green
globes had to suffer from, as two sorts of rotifer were frequently met
with. One of these was a very handsome and singular creature, which in
some positions had the general contour of a cockatoo, only that the legs
were wanting, and the head exhibited a monkey face. The "wheels" were
represented by ciliary tufts, and two bright red eyes twinkled with a
knowing look. From each shoulder proceeded a long curved spine, and
about two thirds down the body, and lying between the two long spines, a
shorter one was articulated, which followed the same curve. A gizzard
was busy in the breast, and the body terminated in two short toes, which
grasped a large round egg. Whenever the cilia were drawn in, the three
spines were thrown up; but they had an independent motion of their own,
and every now and then were jerked suddenly and violently back, which
occasioned a rapid change in the creature's position. The gizzard
appeared to consist of two rounded masses, having several ridges of
teeth, which worked against each other something like the prominences of
a coffee-mill. From the three spines, this animal was a _Triarthra_, or
Three-limbed Rotifer, but the position of the spines, and the toes, made
it differ from any species described in the 'Micrographic Dictionary,'
or in Pritchard.
Whether or not this species is to be regarded as having a lorica or not,
must depend upon the precise meaning attached to that word. At any rate
the integument was much firmer than in many of the rotifers, and gave an
efficient support to the spines which a mere skin could not do. As Mr.
Gosse remarks of an allied genus, the _Polyarthra_, or Many-limbed
Rotifer, this creature could not be investigated without coming to the
conclusion "Here again we have true jointed limbs;" a fact of great
importance in determining the zoological rank of the family, and in
supporting Mr. Gosse's view some at least bore a strong affinity with
the group of _Arthropoda_, of which the insects are the principal
representatives.
[Illustration: Brachionus urceolaris. This drawing has been accidentally
reversed by the engraver, which alters the relative place of the
internal organs.]
Another rotifer of even greater interest, which was busy among the
Cryptomonads, was the Brachion, or "Pitcher Rotifer" (Brachionus). The
members of this genus will frequently reward the searcher into
pond-life. Their main characteristic is a cup or pitcher-shaped lorica,
which is cut or notched at the top into several horns or projections,
the number of which indicates the species; while two or more similar
projections ornament the bottom. This lorica is like the shell of a
tortoise open at both ends; from the top an extremely beautiful wreath
of cilia is protruded, and also some longer and stiff cilia, or slender
spines, which do not exhibit the rotatory movement. The ciliary
apparatus is in reality continuous, but it more often presents the
appearance of several divisions, and the lateral cilia frequently hang
over the sides. From the large size of each cilium they are very
favorable creatures for exhibiting the real nature of the action, which
gives rise to the rotatory appearance, and which can be easier studied
than described. By movements, partly from their base, and partly arising
from the flexibility of their structure, the cilia come alternately in
and out of view, and when set in a circular pattern, the effect is
amazingly like the spinning round of a wheel. The internal arrangements
of the Brachiones are finely displayed, and they have a most aldermanic
allowance of gizzard, which extends more than half way across each side
of the median line, and shows all the portions described by Mr. Gosse.
As the joints of this machine move, and the teeth are brought together,
one could fancy a sound of mill-work was heard, and the observer is
fully impressed with a sense of mechanical power.
When the creature is obliging enough to present a full front view, her
domestic economy is excellently displayed. The prey that is caught in
her whirlpool is carried down by a strong ciliary current to the
gizzard, which may be often seen grappling with objects that appear much
too big for its grasp; and Mr. Gosse was lucky in witnessing an attempt
to chew up a morsel that did actually prove too large and too tough, and
which, after many ineffectual efforts, was suddenly cast out. As soon as
food has passed the gizzard, it is assisted in its journey by more
ciliary currents, which are noticeable in the capacious stomach, in the
neighbourhood of which the secreting and other vessels are readily
observed. Just over the gizzard blazes a great red eye, of a square or
oblong form, and it reposes upon a large mass of soft granular-looking
brain, which well justifies Mr. Gosse's epithet "enormous." Whether this
brain is highly organized enough to be a _thinking_ apparatus, we do not
know, but it is evidently the cause of a very vigorous and consentaneous
action of the various organs the Brachion possesses.
A description of the Brachion would be very incomplete if it omitted
that important organ the tail, which in this family reaches the highest
point of development. It is a powerful muscular organ, of great size in
proportion to the animal, capable of complete retraction within the
carapace, and of being everted wholly, or partially, at will. It
terminates in two short conical toes, protruded from a tube-like sheath,
and capable of adhering firmly even to a substance so slippery as glass.
This tail may be observed to indicate a variety of emotions, if we can
ascribe such feelings to a rotifer, and it answers many purposes. Now we
see it cautiously thrust forth, and turned this way and that, exploring
like an elephant's trunk, and almost as flexible. Now it seizes firm
hold of some substance, and anchors its proprietor hard and fast. A few
moments afterwards it lashes out right and left with fury, like the tail
of a cat in a passion. Then again it will be retracted, and a casual
observer might not imagine the Brachion to be furnished with such a
terminal implement.
The Brachiones may often be seen with one or more large eggs stuck
about the upper part of the tail, and others may be discerned inside.
One specimen before us has three eggs attached to her in this way. They
are large oval bodies, with a firm shell. These creatures differ very
much in appearance, according to the direction in which they are seen,
and a side view makes them look so different from a full front or back
aspect, that it would be easy to suppose another animal was under
observation. The extent to which the ciliary apparatus is protruded, and
the pattern it forms likewise differs continually; and hence no drawing,
however correct, is sure to resemble the arrangement that may be
presented to the observer's eye. But however our little "Pitcher" may be
viewed, it is sure to prove a spectacle of interest and delight.