SEPTEMBER.
Microscopic value of little pools--Curious facts in appearance
and disappearance of Animalcules and Rotifers--Mode of
preserving them in a glass jar--Fragments of Melicerta
tube--Peculiar shape of Pellets--Amphileptus--Scaridium
Longicaudum--A long-tailed Rotifer--Stephanoceros Eichornii--A
splendid Rotifer--Its gelatinous bottle--Its crown of
tentacles--Retreats on alarm--Illumination requisite to see its
beauties--Its greediness--Richly-coloured Food--Nervous ganglia.
Scattered about Hampstead Heath are a number of little pools, not big
enough to be dignified by the name of ponds. They are generally
surrounded by furze bushes, and would escape attention if not actually
looked for. Those which are mere puddles, and have only a brief
existence in rainy weather, seldom reward the labour of investigation;
but others are permanent, except after prolonged drought, and afford
convenient situations for the growth of confervae, star-weed, and other
plants. These will nearly always repay the microscopic collector during
the winter, when he must break the ice to get at their contents; in
spring, when long chains of frog-spawn afford ocular evidence of the
prolific properties of the Batrachian reptiles; and in summer, when
they afford both shade and sunshine to their numerous inhabitants. Small
beetles, water-spiders, larvae of gnats, and other insects, rotifers,
including the tubicolar sorts, and several varieties of infusoria may be
expected and generally found. There is, however, a curious fact about
ponds, big and little, which Pritchard remarks upon in his 'Infusoria,'
and which corresponds with our own experience, that those which have
proved to be well stocked with any particular creature during one year,
will very likely contain none of it in the next. There are of course
exceptions to this rule, but we have often been astonished and
disappointed at finding the complete change, both in populousness and
population, that a revolution of twelve months will make; and it would
be extremely interesting to notice the changes that took place during a
term of years.
Such researches might unfold some unexpected laws in the succession of
infusorial life. Those germs which are most widely diffused, will be the
most likely to be developed in any mass of convenient water; but how and
why the rarer forms come and go is very imperfectly understood. Slight
modifications in surrounding circumstances will materially affect the
result. Thus, if we bring home a handful of conferva, and a few
water-plants of higher organisation, such as duckweed and anacharis, and
place the whole in a glass jar full of pond-water, we shall at first
have a good stock of objects; but they will usually grow less and less,
until scarcely anything is left. If, however, we introduce a few pieces
of straw, or a tiny wisp of hay, we shall succeed much better, and not
only preserve our population longer, but enjoy a succession of animated
crops. Extensive decomposition of vegetable matter kills off all but
certain families, such as Paramecia, who enjoy it; on the other hand,
too little decomposition proves fatal to some creatures, by depriving
them of their food, and when they have died off, those who depended upon
them for a living, die too. Different vegetables in decomposition suit
different creatures, and hay and straw in that state seem to please the
largest number. An animalcule tank will succeed best when it contains
two or three kinds of growing plants, which oxygenize the air, and a
moderate variety of decomposing organisms will supply food without
making the water offensive.
From these considerations it will be apparent that not only the nature
of the vegetation of a pond, which is often changed by accidental
circumstances, but also the quality of the odds and ends that the winds
may blow into it, or which may fall through the air, will do much to
determine the character and number of its inhabitants, while the
quantity of shade or sunshine it enjoys, will also exercise an important
influence. Hay and other infusions have from the beginning of
microscopic investigations been employed to obtain the creatures which
the Germans call "Infusions thierchen" (infusion animalcules), and the
English "Infusoria;" but very little has yet been done in the way of
their scientific culture and management.
To return from this digression to our little Hampstead ponds, we
obtained from one, in September, that was full of star-weed, a number of
sugar-loaf bodies, adhering to one another, and of a pale yellow brown
colour. The specimens first examined looked complete in themselves, and
were taken for eggs of some water creature. Further search, however,
disclosed aggregations of similar sugar-loaves that had evidently formed
part of a tubular structure, and the idea at once occurred that they
were fragments of a Melicerta tube, a conclusion that was verified by
finding some tubes entire and a dead Melicerta in the rubbish at the
bottom. All the specimens of Melicerta tubes we had hitherto examined
were composed of _rounded_ pellets, but these were made of pointed cones
or sugar-loaves, with the points projecting outwards from the general
surface. In Pritchard's 'Infusoria,' these pellets are described "as
small lenticular bodies." The 'Micrographic Dictionary' states that the
tubes of the Melicerta are composed of "numerous rounded or discoidal
bodies;" and Mr. Gosse, in his 'Tenby,' which contains an admirable
description, and an exquisite drawing of this interesting rotifer, calls
the pellets "round."
[Illustration: Melicerta ringens.]
Not being able to obtain a living specimen of the Melicerta, who made
her tube of long sugar-loaves, I could not tell whether she differed in
structure from the usual pattern of her race, but the general appearance
of the dead body was the same. It is possible that these creatures
possess some power of modifying the form of their singular bricks, or
they may at different ages vary the patterns, which matters some
fortunate possessor of a colony of these animals may be able to
verify.
[Illustration: Scaridium longicaudum.]
In the sediment of the water containing the Melicerta cases was found an
animalcule about 1--120" long, covered with cilia, and having a
proboscis seldom more than a quarter of the length assumed by the body,
which continually changed its form, sometimes elongating, sometimes
shortening, and often contracting one side into a deep fissure. It was,
probably, an _Amphileptus_, though not precisely agreeing with any
drawing or description I am acquainted with. Another inmate of the same
water was a lively long-tailed rotifer, with a small oval body, a tuft
of vibrating cilia and a curved bristle visible among them on one side.
This creature had a jointed tail-foot, ending in two long style-shaped
toes, and by means of this appendage executed rapid leaps or springs. It
was the _Scaridium longicaudum_, and agreed in dimensions tolerably well
with the size given in the books, namely, total length 1--72". With a
power of five hundred diameters the muscles of the tail-foot presented
a beautifully striated appearance.
Towards the end of the month I passed the Vale of Heath Pond, Hampstead,
and although I had not gone out for the purpose of collecting, was
fortunately provided with a two-dram bottle. Close by the path the
_Anacharis alsinastrum_ grew in profusion, quantities of water-snails
crawled among its branches, and small fish darted in and out, threading
their mazes with lightning rapidity. Thrusting a walking-stick among the
mass of vegetation, a few little tufts were drawn up and carefully
bottled, with the addition of a little water. Returning home, a few
leaves were placed in the live-box, and on examination with the power of
sixty diameters they disclosed a specimen of, perhaps, the most
beautiful of all the rotifers, the _Stephanoceros Eichornii_. In this
elegant creature an oval body, somewhat expanded at the top, is
supported upon a tapering stalk, and stands in a gelatinous bottle,
composed of irregular rings superimposed one upon the other, as if
thrown off by successive efforts, the upper ones being inverted and
attached to the body of the animal. But that which constitutes the glory
of this little being is the crown of five tapering tentacles, each
having two rows of long cilia arranged on opposing sides, but not in the
same plane. The ordinary position of the tentacles is that of a graceful
elliptical curve, first swelling outwards, then bending inwards, until
their points closely approximate, but each is capable of independent
motion, and they are seldom quiet for many minutes at a time. The cilia
can be arranged in parallel rows or in tufts at the will of the
creature, and their motion appears under control, and susceptible of
greater modification than is exhibited by the ordinary infusoria.
[Illustration: Stephanoceros Eichornii.]
The Stephanoceros is a member of the Floscule family, but in all the
specimens I obtained and watched for several weeks, there was an
important difference in the relation of the tube to the creature. In the
Floscules I had never seen anything like an adhesion between the tube
and the animal, but in the Stephanoceros I noticed it continually, and
always in the manner already described. Like the Floscule, the
Stephanoceros is readily alarmed, and retreats into her house, carrying
with her the invaginated portion. In the last edition of 'Pritchard's
Infusoria,' this case is spoken of as apparently not tubular, but a
solid gelatinous mass, enveloping the animal as high up as the base of
the rotatory arms. It is very likely that specimens at different ages,
and possibly in different seasons, may vary in the structure of their
abodes; but I am not able to concur in the preceding account, as all the
tubes I examined resembled sacks turned in at the mouths, and attached
to the shoulders only of their inmates; and on one occasion I was able
to look down into a deserted tube, which had not collapsed, as it would
have done if it had been merely a solid gelatinous mass.
Like the Floscule, the Stephanoceros only reveals her beauties under
careful illumination. A direct light renders them invisible, and only
when the requisite obliquity has been obtained, does the exquisite
character of the structure become displayed. The dark-ground
illumination is very useful, and makes the ciliary action very distinct.
At times a view can be obtained, in which the cilia of perhaps a single
tentacle are all ranged like the steel springs of a musical box. For a
moment they are quiescent, and then they vibrate in succession, each
moving thread sparkling in the light. With a clumsy mode of lighting
them, the cilia look like stumpy bristles, and are often so drawn; but
precisely the right quantity of light coming in the right direction,
makes them appear more numerous, and much longer than would at first be
supposed. When well exhibited the tentacles have a lustre between glass
and pearl; the body, in a favorable specimen, is like a crystal cup, and
the food, usually composed of small red and green globes, glows like
emeralds and rubies, as if in the height of luxury the little epicure
had more than rivalled Cleopatra's draught, and instead of dissolving,
swallowed its jewelry whole. So lustrous and varied in colour is the
whole appearance of the animal under these circumstances, that it is
frequently alluded to by one of our first artists, to whom it was
displayed.
It is said by some authors that the tentacles are used to seize prey.
This never occurred under my observation, although their basal portions
are often approximated when an object is forced down to the grinding
apparatus below. The Stephanoceros is a ravenous feeder, and swallows a
variety of creatures. Green vegetable monads, rich red and brown globes
of similar characters, and any animalcule that comes in her way is
acceptable; and even good-sized rotifers do not escape her
all-consuming maw. On one occasion I noticed one of the loricated sort,
more than half as long as one of her tentacles, rapidly swallowed, and
passed downwards without attempting to escape. Objects much too big for
the gizzard are often gulped down, and probably receive a preliminary
softening and maceration in the crop. Very often, when food is
plentiful, the creature is filled to the brim, but still endeavours to
continue her abundant meal. From the presence of large quantities of
food and the density of the integuments, the gizzard cannot always be
seen; but in favorable specimens its teeth may be observed busily at
work.
At the base of the tentacles small masses of matter may be discovered,
which are probably nervous ganglia, and other organs; and Ehrenberg
discovered small vibrating bodies, supposed to be connected with the
function of respiration. A single egg, as shown in the annexed drawing,
is often found, and the ovarian is said to develop but few at a time.
Two red eyes are found in young specimens, but in adults they either
disappear or are not conspicuous. The Stephanoceri are sociable animals,
and when one is found, others are probably near at hand. Several may
often be discovered on the same branch of a small water-plant, of
various dimensions, and in different stages of growth. The full size is
about 1--36" in height, and from its magnitude care is required not to
crush it in the live-box. When specimens are plentiful, some should be
placed in that convenient receptacle; and others with the plant on which
they are growing, in a glass cell or trough, where they have more room
to display their motions, and can with fresh supplies of water, be
preserved for days and weeks. With occasional renewals from one pond, I
was able to keep up a stock for about three months, and never had
objects which gave more pleasure to myself or to my friends.