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MARVELS OF POND-LIFE
OR,
A YEAR'S MICROSCOPIC RECREATIONS
AMONG THE
POLYPS, INFUSORIA, ROTIFERS, WATER-BEARS, AND POLYZOA.
BY
HENRY J. SLACK, F.G.S.,
SECRETARY TO THE ROYAL MICROSCOPICAL SOCIETY;
AUTHOR OF
'THE PHILOSOPHY OF PROGRESS IN HUMAN AFFAIRS,' ETC. ETC.
_SECOND EDITION._
ILLUSTRATED WITH COLOURED PLATES AND NUMEROUS
WOOD ENGRAVINGS.
LONDON:
GROOMBRIDGE AND SONS,
5, PATERNOSTER ROW.
MDCCCLXXI.
PRINTED BY J. E. ADLARD,
BARTHOLOMEW CLOSE.
INTRODUCTION.
As this little book is intended to be no more than an introduction to an
agreeable branch of microscopical study, it is to be hoped it will not
require a formal preface; but a few words may be convenient to indicate
its scope and purpose.
The common experience of all microscopists confirms the assertion made
by Dr. Goring, that the most fascinating objects are living creatures of
sufficient dimensions to be easily understood with moderate
magnification; and in no way can objects of this description be so
readily obtained, as by devoting an occasional hour to the examination
of the little ponds which are accessible from almost any situation. A
complete volume of pond lore would not only be a bulky book--much bigger
than the aldermanic tomes which it is the fashion to call "Manuals,"
although the great stone fists in the British Museum would be required
to grasp them comfortably,--but its composition would overtask all the
philosophers of our day. In good truth, a tea-spoonful of water from a
prolific locality often contains a variety of living forms, every one of
which demands a profound and patient study, if we would know but a few
things concerning it.
To man, then, is a vast and a minute. Our minds ache at the
contemplation of astronomical immensities, and we are apt to see the
boundless only in prodigious masses, countless numbers, and
immeasurable spaces. The Creative Mind knows no such limitations; and
the microscope shows us that, whether the field of nature's operation be
what to our apprehension is great or small, there is no limit to the
exhibition of marvellous skill. If the "undevout astronomer" be "mad,"
the undevout microscopist must be still more so, for if the matter be
judged by human sense, the skill is greater as the operation is more
minute; and not the sun itself, nor the central orb round which he
revolves, with all his attendant worlds, can furnish sublimer objects of
contemplation, than the miraculous assemblage of forces which make up
the life of the smallest creature that the microscope reveals.
There is an irresistible charm in the effort to trace _beginnings_ in
nature. We know that we can never succeed; that each discovery, which
conducts back towards some elementary law or principle, only indicates
how much still lies behind it: but the geologist nevertheless loves to
search out the first or oldest traces of life upon our globe; and so the
microscopist delights to view the simplest exhibitions of structures and
faculties, which reach their completion in the frame and mind of man.
That one great plan runs through the whole universe is now an
universally accepted truth, and when applied to physiology and natural
history, it leads to most important results.
The researches of recent philosophers have shown us that nature cannot
be understood by studying the parts of animals with reference merely to
their utility in the economy of the creature to which they belong. We
do, indeed, find an admirable correspondence between structures and the
services they perform; but every object in creation, and every part of
it, is in harmonious relation to some grand design, and exhibits a
conformity to some general mode of operation, or some general
disposition and direction of forces, which secures the existence of the
individual or the species, and at the same time works out the most
majestic schemes. Microscopic researches, such as are within the reach
of millions, offer many of the most beautiful illustrations of these
truths; and although the following pages are confined to such objects as
are easily obtainable from ponds, and relate almost exclusively to the
Infusoria, the Rotifers, the Polyps, and the Polyzoa, it is hoped that
they will assist in associating a few of the highly suggestive
reasonings of science, with one of the most pleasurable recreations that
human ingenuity has devised.
After a preliminary chapter, which is intended to assist the young
microscopist in some technical matters, that could not be conveniently
introduced into the text, the observations are distributed in chapters,
corresponding with the twelve calendar months. This arrangement was
suggested by the author's diary of operations for the year 1860, and
although it by no means follows that the months in which particular
creatures were then discovered, will be those in which they will be most
readily found in other years, it was thought advantageous to give a real
account of an actual period of microscopic work, and also that the plan
would facilitate a departure from the dry manner of a technical
treatise. The index will enable any one to use the book for the purpose
of reference, and it will be observed that the first chapter in which
any member of a group of creatures is introduced, is that in which a
general description of the class is given. The illustrations are taken
from drawings made by the wife of the author from the actual objects,
with the exception of a few instances, in which the authority is
acknowledged. The sketches were made _especially for beginners_, and the
rule followed, was not to introduce any details that could not be seen
at one focus, and with the simplest means: more elaborate
representations, though of the highest value to advanced students, are
bewildering at the commencement.
The ponds referred to are all either close to, or within a moderate
distance of, London;[1] but similar objects will in all probability be
obtained from any ponds similarly situated, and the descriptions and
directions given for the capture of the minute prey will be found
generally applicable. Care has been taken throughout to explain the most
convenient methods of examining the objects, and although verbal
descriptions are poor substitutes for the teachings of experience, it is
hoped that those here given will remove some difficulties from a pursuit
that no intelligent person can enter upon without pleasure, or consent
to abandon when its elementary difficulties have been mastered, and the
boundless fields of discovery are opened to view. Let not the novice be
startled at the word "discovery." It is true that few are likely to
arrive at new principles or facts which will inscribe their names upon
the roll of fame; but no one of ordinary powers can look at living
objects with any considerable perseverance, without seeing much that has
never been recorded, and which is nevertheless worthy of note; and when
the mind, by its own exertions, first arrives at a knowledge of new
truth, an emotion is felt akin to that which more than recompenses the
profoundest philosopher for all his toil.
[1] Many are now (1871) destroyed by the progress of building.
CONTENTS.
CHAPTER I.
MICROSCOPES AND THEIR MANAGEMENT.
Powers that are most serviceable--Estimated by Focal
length--Length of Body of Microscope and its Effects--Popular
Errors about Great Magnification--Modes of Stating Magnifying
Power--use of an "Erector"--Power of various Objectives with
different Eye-pieces--Examination of Surface Markings--Methods
of Illumination--Direct and Oblique Light--Stage
Aperture--Dark-ground Illumination--Mode of Softening
Light--Microscope Lamps--Care of the Eyes
CHAPTER II.
JANUARY.
Visit to the Ponds--Confervae--Spirogyra
quinina--Vorticella--Common Rotifer--Three Divisions of
Infusoria--Phytozoa--Protozoa--Rotifera--Tardigrada--Meaning of
these Terms--Euglenae--Distinction between Animals and
Vegetables--Description of Vorticellae--Dark-ground
Illumination--Modes of producing it--The Nucleus of the
Vorticella--Methods of Reproduction--Ciliated
Protozoa--Wheel-bearers or Rotifers--Their Structure--The Common
Rotifer--The young Rotifer seen inside the old one--an Internal
Nursery--"Differentiation" and "Specialization"--Bisexuality of
Rotifers--Their Zoological Position--Diversities in their
Appearance--Structure of their Gizzard--Description of Rotifers
CHAPTER III.
FEBRUARY.
Visit to Hampstead--Small
ponds--Water-Fleas--Water-Beetle--Snails--Polyps--Hydra
viridis--The Dipping-tube--A Glass Cell--The Hydra and its
Prey--Chydorus Sphaericus and Canthocamptus, or Friends and their
Escapes--Cothurnia--Polyp Buds--Catching Polyps--Mode of Viewing
Them--Structure of Polyps--Sarcode--Polyps Stimulated by
Light--Are they Conscious?--Tentacles and Poison
Threads--Paramecium--Trachelius--Motions of Animalcules, whether
Automatic or directed by a Will--Their Restless Character
CHAPTER IV.
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
CHAPTER V.
APRIL.
The Beautiful Floscule--Mode of Seeking for Tubicolar
Rotifers--Mode of Illuminating the Floscule--Difficulty of
seeing the Transparent Tube--Protrusion of Long
Hairs--Lobes--Gizzard--Hairy Lobes of Floscule not Rotatory
Organs--Glass Troughs--Their Construction and Use--Movement of
Globules in Lobes of Floscule--Chaetonotus larus--Its mode of
Swimming--Coleps hirtus--Devourer of Dead Entomostraca--Dead
Rotifer and Vibriones--Theories of Fermentation and
Putrefaction--Euplotes and Stylonichia--Fecundity of Stylonichia
CHAPTER VI.
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
Parasytic Epistylis like the "Old Man of the Sea"--Halteria and
its Leaps--Aspidisca lynceus
CHAPTER VII.
JUNE AND JULY.
Lindia torulosa--OEcistes crystallinus--A Professor of
Deportment on Stilts--Philodina--Changes of Form and
Habits--Structure of Gizzard in Philodina Family--Mr. Gosse's
Description--Motions of Rotifers--Indications of a Will--Remarks
on the Motions of Lower Creatures--Various Theories--Possibility
of Reason--Reflex Actions--Brain of Insects--Consensual
Actions--Applications of Physiological Reasoning to the
Movements of Rotifers and Animalcules
CHAPTER VIII.
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
CHAPTER IX.
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
CHAPTER X.
OCTOBER.
Stentors and Stephanoceri--Description of Stentors--Mode of
viewing them--Their Abundance--Social Habits--Solitary Stentors
living in Gelatinous Caves--Propagation by Divers
Modes--Cephalosiphon limnias--A Group of Vaginicolae--Changes of
Shape--A Bubble-blowing Vorticella
CHAPTER XI.
NOVEMBER.
Characteristics of the Polyzoa--Details of Structure according
to Allman--Plumatella repens--Its Great Beauty under proper
Illumination--Its Tentacles and their Cilia--The Mouth and its
Guard or Epistome--Intestinal Tube--How it swallowed a Rotifer,
and what happened--Curiosities of Digestion--Are the Tentacles
capable of Stinging?--Resting Eggs, or "Statoblasts"--Tube of
Plumatella--Its Muscular Fibres--Physiological Importance of
their Structure
CHAPTER XII.
DECEMBER.
Microscopic Hunting in Winter--Water-Bears, or Tardigrada--Their
Comical Behaviour--Mode of viewing them--Singular
Gizzard--Wenham's Compressorium--Achromatic Condenser--Mouth of
the Water-Bear--Water-Bears' Exposure to Heat--Soluble
Albumen--Physiological and Chemical Reasons why they are not
killed by Heating or Drying--The Trachelius ovum--Mode of
Swimming--Method of Viewing--By Dark-ground
Illumination--Curious Digestive Tube with
Branches--Multiplication by Division--Change of Form immediately
following this Process--subsequent Appearances
CHAPTER XIII.
CONCLUSION.--Remarks on Classification, &c.
MARVELS OF POND-LIFE.
CHAPTER I.
PLAIN HINTS ON MICROSCOPES AND THEIR MANAGEMENT.
Powers that are most serviceable--Estimated by focal
length--Length of body of microscope and its effects--Popular
errors about great magnification--Modes of stating magnified
power--Use of an "Erector"--Power of various objectives with
different eye-pieces--Examination of surface markings--Methods
of illumination--Direct and oblique light--Stage aperture--Dark
ground illumination--Mode of softening light--Microscope
lamps--Care of the eyes.
The microscope is rapidly becoming the companion of every intelligent
family that can afford its purchase, and, thanks to the skill of our
opticians, instruments which can be made to answer the majority of
purposes may be purchased for three or four guineas, while even those
whose price is counted in shillings are by no means to be despised. The
most eminent English makers, Wales, and Tolles, in America, and
Hartnack, in Paris, occupy the first rank, while the average productions
of respectable houses exhibit so high a degree of excellence as to make
comparisons invidious. We shall not, therefore, indulge in the praises
of particular firms, but simply recommend any reader entering upon
microscopic study to procure an achromatic instrument, if it can be
afforded, and having at least two powers, one with a focus of an inch or
two thirds of an inch, and the other of half or a quarter. Cheap
microscopes have usually only one eye-piece, those of a better class
have two, and the best are furnished with three, or even more.
The magnifying power of a compound microscope depends upon the focal
length of the object-glass (or glass nearest the object), upon the
length of the tube, and the power of the eye-piece. With regard to
object-glasses, those of shortest focal length have the highest powers,
and the longest eye-pieces have the lowest powers. The body of a
microscope, or principal tube of which it is composed, is, in the best
instruments, about nine inches long, and a draw tube, capable of being
extended six inches more, is frequently useful. From simple optical
principles, the longer the tube the higher the power obtained with the
same object-glass; but only object-glasses of very perfect construction
will bear the enlargement of their own imperfections, which results from
the use of long tubes; and consequently for cheap instruments the
opticians often limit the length of the tube, to suit the capacity of
the object-glasses they can afford to give for the money. Such
microscopes may be good enough for the generality of purposes, but they
do not, with glasses of given focal length, afford the same magnifying
power as is done by instruments of better construction. The best and
most expensive glasses will not only bear long tubes, but also
eye-pieces of high power, without any practical diminution of the
accuracy of their operation, and this is a great convenience in natural
history investigations. To obtain it, however, requires such perfection
of workmanship as to be incompatible with cheapness. An experienced
operator will not be satisfied without having an object-glass at least
as high as a quarter, that will bear a deep eye-piece, but beginners are
seldom successful with a higher power than one of half-inch focus, or
thereabouts, and before trying this, they should familiarise themselves
with the use of one with an inch focus.
It is a popular error to suppose that enormous magnification is always
an advantage, and that a microscope is valuable because it makes a flea
look as big as a cat or a camel. The writer has often smiled at the
exclamations of casual visitors, who have been pleased with his
microscopic efforts to entertain them. "Dear me, what a wonderful
instrument; it must be immensely powerful;" and so forth. These
ejaculations have often followed the use of a low power, and their
authors have been astonished at receiving the explanation that the best
microscope is that which will show the most with the least
magnification, and that accuracy of definition, not mere increase of
bulk, is the great thing needful.
Scientific men always compute the apparent enlargement of the object by
_one_ dimension only. Thus, supposing an object one hundredth of an inch
square were magnified so as to appear one inch square, it would, in
scientific parlance, be magnified to "one hundred diameters," or one
hundred linear; and the figures 100 would be appended to any drawing
which might be made from it. It is, however, obvious that the length is
magnified as well as the breadth; and hence the magnification of the
whole surface, in the instance specified, would be one hundred times one
hundred, or ten thousand: and this is the way in which magnification is
popularly stated. A few moments' consideration will show that the
scientific method is that which most readily affords information. Any
one can instantly comprehend the fact of an object being made to look
ten times its real length; but if told that it is magnified a hundred
times, he does not know what this really means, until he has gone
through the process of finding the square root of a hundred, and learnt
that a hundredfold magnification means a tenfold magnification of each
superficial dimension. If told, for example, that a hair is magnified
six hundred diameters, the knowledge is at once conveyed that it looks
six hundred times as broad as it is; but a statement that the same hair
is magnified three hundred and sixty thousand times, only excites a
gasping sensation of wonder, until it is ascertained by calculation that
the big figures only mean what the little figures express. In these
pages the scientific plan will always be followed.
If expense is not an object, a binocular instrument should be purchased,
and it is well to be provided with an object-glass as low as three or
even four inches focus, which will allow the whole of objects having the
diameter of half an inch or more to be seen at once. Such a low power
is exceedingly well adapted for the examination of living insects, or of
the exquisite preparations of entire insects, which can now be had of
all opticians. Microscopes which have a draw tube can be furnished with
an _erector_, an instrument so called because it erects the images,
which the microscope has turned upside down, through the crossing of the
rays. This is very convenient for making dissections under the
instrument; and it also gives us the means of reducing the magnifying
power of an object-glass, and thus obtaining a larger field. The erector
is affixed to the end of the draw tube, and by pulling it out, or
thrusting it in, the rays from the object-glass are intercepted at
different distances, and various degrees of power obtained.
A binocular microscope is most useful with low powers from two thirds
upwards. A new form, devised by Mr. Stephenson, acts as an erector, and
is very valuable for dissections. It works with high powers.
Beginners will be glad to know how to obtain the magnifying power which
different objects require, and it may be stated that, with a full-sized
microscope, a two-inch object-glass magnifies about twenty-five
diameters with the lowest eye-piece; a one-inch object-glass, or two
thirds, from fifty to sixty diameters; a half-inch about one hundred; a
quarter-inch about two hundred. The use of deeper eye-pieces adds very
considerably to the power, but in proportions which differ with
different makers. One instrument used by the writer has three
eye-pieces, giving with a two thirds object-glass powers of sixty one
hundred and five, and one hundred and eighty respectively; and with a
fifth two hundred and forty, four hundred and thirty, and seven hundred
and twenty, which can be augmented by the use of a draw tube.
It has been well observed that the illumination of objects is quite as
important as the glasses that are employed, and the most experienced
microscopists have never done learning in this matter. Most microscopes
are furnished with two mirrors beneath the stage, one plane and one
concave. The first will throw a few parallel rays through any
transparent object properly placed, and the latter causes a number of
rays to converge, producing a more powerful effect. The first is usually
used in daylight, when the instrument is near a window (one with a north
aspect, out of direct sunlight, being the best); and the second is often
useful when the source of illumination is a candle or a lamp. By varying
the angle of the mirror the light is thrown through the object more or
less obliquely, and its quantity should never be sufficient to pain the
eye. Few objects are seen to the best advantage with a _large_ pencil of
perfectly direct light, and the beginner should practise till the amount
of inclination is obtained which produces the best effect.
It is advisable that the hole in the stage of the microscope should be
large--at least an inch and a half each way--so that the entrance of
oblique rays is not obstructed, and it is desirable that the mirror, in
addition to sliding up and down, should have an arm by which it can be
thrown completely out of the perpendicular plane of the body of the
instrument. This enables such oblique rays to be employed as to give a
dark field, all the light which reaches the eye being _refracted_ by the
object through which it is sent. The opticians sell special pieces of
apparatus for this purpose, but though they are very useful, they do not
render it less desirable to have the mirror mounted as described.
Most microscopes are furnished with a revolving diaphragm, with three
holes, of different sizes, to diminish the quantity of light that is
admitted to the object. This instrument is of some use, and offers a
ready means of obtaining a very soft agreeable light for transparent
objects, viewed with low powers. For this purpose cut a circular disk of
India or tissue paper, rather larger than the biggest aperture; scrape a
few little pieces of spermaceti, and place them upon it, then put the
whole on a piece of writing-paper, and hold it a few inches above the
flame of a candle, moving it gently. If this is dexterously done, the
spermaceti will be melted without singeing the paper, and when it is
cold the disk will be found transparent. Place it over the hole in the
diaphragm, send the light through it, and the result will be a very soft
agreeable effect, well suited for many purposes, such as viewing
sections of wood, insects mounted whole, after being rendered
transparent, many small water creatures, etc. Another mode of
accomplishing this purpose is to place a similarly prepared disk of
paper on the flat side of a bull's-eye lens, and transmit the light of a
lamp through it. This plan may be used with higher powers, and the white
opaque light it gives may be directed at any angle by means of the
mirror beneath the stage.
An ordinary lamp may be made to answer for microscopic use, but one of
the small paraffine lamps now sold everywhere for eighteen-pence is
singularly convenient. It is high enough for many purposes, and can
easily be raised by one or more blocks. A paraffine lamp on a sliding
stand is still more handy, and all the better for a hole with a glass
stopper, through which the fluid can be poured.
Many people fancy that the eyes are injured by continual use of the
microscope, but this is far from being the case if reasonable
precautions are taken. The instrument should be inclined at a proper
angle, all excess of light avoided, and the object brought into focus
before it is steadily looked at. Most people solemnly shut one eye
before commencing a microscopic examination; this is a practical and
physiological mistake. Nature meant both eyes to be open, and usually
resents a prolonged violation of her intentions in this matter. It
requires but a little practice to keep both eyes open, and only pay
attention to what is seen by that devoted to the microscope. The
acquisition of this habit is facilitated, and other advantages gained,
by a screen to keep out extraneous light. For this purpose take a piece
of thin cardboard about nine inches square, and cut a round hole in it,
just big enough to admit the tube of the microscope, about two inches
from the bottom, and equidistant from the two sides. Next cut off the
two upper corners of the cardboard, and give them a pleasant-looking
curve. Then cover the cardboard with black velvet, the commonest, which
is not glossy, answers best, and your screen is made. Put the hole over
the tube of the microscope, and let the screen rest on the little ledge
or rim which forms an ornamental finish to most instruments. A piece of
cork may be gummed at the back of the screen, so as to tilt it a little,
and diminish its chance of coming into contact with that important organ
the nose. This little contrivance adds to the clearness and brilliancy
of objects, and is a great accommodation to the eyes.
One more oculistic memorandum, and we have done with this chapter. Do
not stare at portions of objects that are out of focus, and consequently
indistinct, as this injures the eyes more than anything. Remember the
proverb, "None so deaf as those that won't hear," which naturally
suggests for a companion, "None so blind as those that won't see." It is
often impossible to get every object in the field in focus at one
time;--look only at that which is in focus, and be blind to all the
rest. This is a habit easily acquired, and is one for which our
_natural_ microscopes are exceedingly grateful; and every judicious
observer desires to keep on the best terms with his eyes.