Marvels of Pond-life Part 5

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 c.o.c.katoo, 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 ma.s.ses, 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 princ.i.p.al representatives.

[Ill.u.s.tration: 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 sh.e.l.l 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 pa.s.sed the gizzard, it is a.s.sisted 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 ma.s.s 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 gla.s.s.

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 pa.s.sion. 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 sh.e.l.l. 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.

CHAPTER IX.

SEPTEMBER.

Microscopic value of little pools--Curious facts in appearance and disappearance of Animalcules and Rotifers--Mode of preserving them in a gla.s.s 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-sp.a.w.n afford ocular evidence of the prolific properties of the Batrachian reptiles; and in summer, when they afford both shade and suns.h.i.+ne 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 ma.s.s of convenient water; but how and why the rarer forms come and go is very imperfectly understood. Slight modifications in surrounding circ.u.mstances 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 gla.s.s 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 circ.u.mstances, 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 quant.i.ty of shade or suns.h.i.+ne 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."

[Ill.u.s.tration: 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.

[Ill.u.s.tration: 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 a.s.sumed 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 pa.s.sed 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, quant.i.ties 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 ma.s.s 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 const.i.tutes 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.

[Ill.u.s.tration: 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 inv.a.g.i.n.ated portion. In the last edition of 'Pritchard's Infusoria,' this case is spoken of as apparently not tubular, but a solid gelatinous ma.s.s, 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 ma.s.s.

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 quant.i.ty 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 l.u.s.tre between gla.s.s 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 l.u.s.trous and varied in colour is the whole appearance of the animal under these circ.u.mstances, 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 pa.s.sed 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 quant.i.ties 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 ma.s.ses 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 gla.s.s 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.

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.

October, the finest of our autumn months, is noted for usually granting the inhabitants of our dripping climate about twenty pleasant suns.h.i.+ny days, and it is probably on this account somewhat of a favourite with the infusorial world, although the cold of its nights and early mornings thins their numbers, which reach a maximum in the summer heat. Even in the dismal year 1860, October maintained its character, and afforded a great many opportunities of animalcule hunting, during which a constant supply of Stephanoceri were readily obtained, together with swarms of _Stentors_, which are not exceeded in interest by any of the Ciliated Protozoa. The Stentors were abundant on the same weed (_Anacharis_), that formed the residence of the Stephanoceri, and might be seen in large numbers hanging from it like green trumpets, visible to the una.s.sisted eye. In the 'Micrographic Dictionary' they are said to belong to the Vorticella family, which has already given us several beautiful objects, and possess a marvellous power of changing their shape. It is, however, better to follow Stein, who separates them from the Vorticellids and ranges them in his order Heterotricha, as they have two distinct sets of cilia, small ones covering the body and the larger ones round the mouth. Those before us are named after this property _Stentor polymorphus_,[18] or Many-shaped Stentors, and owe their exquisite tint to numberless green vesicles, or small cavities filled with colouring matter like that of plants. This, however, is not essential to the species which may often be found of other hues. In size this Stentor varies from a hundred and twentieth to one twenty-fourth of an inch. It is entirely covered with fine cilia, disposed in longitudinal rows, and round the head is a spiral wreath of larger and very conspicuous cilia leading to the mouth.

[18] See Frontispiece.

Having observed the abundance of these creatures, a few small branches to which they were appended, were placed in the gla.s.s trough, and viewed with powers of sixty and one hundred linear. Some had tumbled down as shapeless lumps, others presented broad funnel-shaped bodies; while others stretched themselves to great length like the long, narrow post-horns which still wake the echoes of a few old-fas.h.i.+oned towns. The ciliary motion of the elegant wreath was active and rapid, causing quite a stir among all the little particles, alive and dead; and when the right sort of food came near the corkscrew entrance to the mouth, down it went, and if conspicuous for colour, was subsequently seen apparently embedded in little cavities, which Ehrenberg supposed were separate stomachs, although that theory is now rejected. One advantage of viewing these objects in a sufficient quant.i.ty of water, to leave them in freedom, is that they frequently turn themselves, so that you can see right down into them; and the drawing given in the frontispiece represents such a view, which is the most favorable for the exhibition of the mouth. To make out the details of their structure, to see the nucleus and other organs, the flattening in the live-box is useful, and it enables much higher powers to be employed.

[Ill.u.s.tration: A, B, C, D, Stentor polymorphus in different degrees of expansion. A large specimen is one twenty-fourth of an inch long.]

After leaving the Anacharis in a gla.s.s jar for a few days, the Stentors multiplied exceedingly; some clung to the sides of the vessel in sociable communities, others hung from the surface of the water, and crowds settled upon the stems, visibly changing their tint, as the Stentor green was much bluer than that of the plant. Scores swam about in all sorts of forms. Now they looked like cylindrical vessels with expanding brims, now globular, now oddly distorted, until all semblance of the original shape was lost. Many were found in s.h.i.+ny tubes, but these were never so lively or green as the free swimmers, but mostly of a dingy dirty hue.

These housekeepers were more timid and cautious than the roving tribe.

They came slowly out of their dens, drew back at the slightest alarm, never took their tails from home, and only extended their full length when certain not to be disturbed. Some authors have thought they only take to private lodgings when they feel a little bit poorly, but others dispute this opinion, and I do not think it is correct. I have found these Stentors at all seasons, from January to the autumn, but they are never so numerous, nor aggregated in numbers like the roving sort.

Whether they are old folks, who are tired of the world and its gaieties, and devote the remainder of their lives to contemplation, or whether they are bachelors disappointed in love, I am unable to say; but they are very inferior in beauty to the "gay and glittering crowd."[19]

[19] Stein says the colourless variety of S. Polymorphus is sometimes found with a tube, and the S. Rossellii very frequently so provided.

For some weeks my Stentors abounded, and then most of them suddenly disappeared. They could not have "moved," but probably "went to smash"

by a process peculiar to infusoria, and which Dujardin politely describes as "diffluence." This mode of making an exit from the stage of life is more tragical than the ripping up so fas.h.i.+onable in j.a.pan. The integument bursts, and its contents disperse in minute particles, that in their turn disappear, and scarcely leave a "wrack behind."

The Stentors obey the injunction to "increase and multiply" by self-division, which Stein says is always oblique, and the nucleus, which plays such an important part in infusoria, is band-like, moniliform (bead-shape), or round. When an animalcule increases by self-division, a portion of the nucleus goes with each part, and it is probably the organ which stimulates the change. It is also concerned in other modes of propagation. "The a.n.u.s is situated on the back close beneath the ciliary circle;" and the "contractile vesicle on a level with the ciliary wreath." Stein records that in November, 1858, he met green Stentors (_Polymorphus_) encysted, and he figures one in a gelatinous flask having a stopper in its narrow neck.

Before closing our account of the Stentor, let us revert a moment to the ciliary wreath, as it may be made the subject of a curious experiment.

If, for example, the cilia are viewed at right-angles to their length, they will seem to form a delicate frill, in which a quivering motion is perceived. But if the table is shaken by a sharp blow, the frill is thrown into waves, or takes the form which washerwomen give to certain female articles by the use of the Italian iron, and the ciliary motion is thus made to take place in different planes, and rendered strikingly apparent.

One day turning over the Anacharis in search of subjects, a small brown tube was noticed, from which a gla.s.sy rod protruded like the feeler of a rotifer. Keeping the table quiet, and watching the result, was soon rewarded by a further protrusion of the feeler, accompanied by a portion of the body of the inmate of the tube. The feeler was thrust on this side and on that, as if collecting information for its proprietor, who, I suppose, was satisfied with the intelligence, and gradually extended herself, until she stood out two thirds in length beyond the tube, and set two lobes of one nearly continuous ciliary organ in rapid motion.

Sometimes the creature, _Cephalosiphon limnias_, bent its neck, if I may so speak, to the right, and sometimes to the left, and sometimes stood upright, when the true form of the ciliary apparatus could be seen. The tube of this creature was opaque, from the adhesion of foreign matter, and presented an untidy appearance, strangely contrasting with the clear, neat bottles of the Floscules. These Cephalosiphons are very whimsical in their ways, and many that were sent to different observers never exhibited their ciliary wreaths, but performed sundry antics, disguising their true shape.