Marvels of Pond-life Part 4

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 cla.s.s 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 a.s.sume larger dimensions.

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.

A Pressure of other occupations prevented full use being made of June and July, nor was the weather at all propitious. For this reason the microscopic doings of these two months are recorded in one chapter.

As usual the Kentish Town ponds were productive of objects, and among them were several rotifers not found in the previous months. The first of these was a very small worm-like thing, with one eye, a tuft of cilia about the mouth, and two toes at the tail end. Had it not been for the jaws, which were working like fingers thrust against each other, and which were unmistakably of the rotifer pattern, the animal might have been supposed to belong to some other cla.s.s. According to the 'Micrographic Dictionary,' the _Lindia torulosa_ is 1--75" long, but this specimen was only about 1--200". It was possibly very young, and did not thrust out its cilia in two distinct tufts, as Cohn describes, although it may have had the power of doing so. At times it sprang quickly backwards and forwards, bringing its head where its tail was before. This object required for its comfortable elucidation a power of about six hundred linear.

[Ill.u.s.tration: OEcistes crystallinus.]

Among the common water-plants, which are worth examining as the probable abodes of rotifers or infusoria, is the pretty little thing called "star-weed," some of which was obtained from the last-mentioned ponds, and on examination yielded a specimen of a tube-dwelling rotifer, the _OEcistes crystallinus_, which, although less beautiful than the Floscules or the Melicerta, is, nevertheless, a pretty and interesting object. In this instance a little rough dirty tube, about 1--70" long, was observed to contain an animal capable of rising up and expanding a round mouth garnished with a wreath of cilia; while a little below, the indefatigable and characteristic gizzard of the tribe was in full play.

A power of two hundred and forty linear sufficed to afford a good view, and it was seen that a long, irregular, conical body was supported upon a short wrinkled stalk. The usual drawings represent this creature with a short bell-shaped body upon a very long slender pedicle. Possibly this one might have been able to show himself under this guise, but he did not attempt it; his appearance being always pretty much as described, which made the foot shorter and the body longer than the measurements which naturalists have given, and according to which the whole creature is 1--36" long, although the body is only 1--140". The tube of the _OEcistes_ is called a "lorica," or carapace; but it has in truth no right whatever to the appellation.

Another strange rotifer, of whose name I am uncertain, had an ovalish oblong body, and a pair of legs like compa.s.ses, twice as long as himself. His antics were those of a posture-master, or "Professor of Deportment" on stilts. Sometimes he stood bolt upright, bringing his legs close together; then they were jauntily crossed, and the body carried horizontally; then the two legs would be slightly opened, and the body thrown exactly at right-angles to them. These antics were repeated all the while the observation lasted, and had a very funny effect in proving that drollery is practised, if not understood, in the rotatorial world.

[Ill.u.s.tration: Philodina (swimming).]

Another kind of rotifer was abundant--the _Philodina_, which belongs to the same family as the common wheel-bearer, namely, the _Philodinaea_.

The _Philodina_ is a good deal like the common wheel-bearer, or _Rotifer vulgaris_, but is usually of a stouter build, and carries his eyes in a different place. In the common rotifer these organs are situated on the proboscis, while those of the Philodina are lower, and said to be "cervical." The changes of form in this rotifer are still more remarkable than in the common wheel-bearer. When resting it resembles a pear-shaped purse, puckered in at the mouth. Then it thrusts out its tail-foot, swells its body to an oval globe, protrudes its feeler, and slightly exposes a row of cilia. After this two distinct wheels are everted, and as their cilia whirl and spin, the animal is swiftly rowed along, until it thinks proper to moor itself fast by the tail-foot, and employ all its ciliary power in causing currents to converge towards its throat. When it pleases it can elongate the body, till it becomes vermiform, and it walks like the common rotifer, by curving its back, and bringing its nose and its tail in contact with the ground.

[Ill.u.s.tration: Philodina (crawling).]

The gizzard of this family (_Philodinaea_) presents a considerable deviation from the perfect form exhibited by the _Brachions_. According to Mr. Gosse, "The _mallei_ and the _incus_ (terms already explained) are soldered together into two subquadrantic-globular ma.s.ses, which appear to be muscular, but invested with a solid integument. The _manubria_ (handles) may still be recognised in a vertical aspect as three loops, of which the central one is chiefly developed, and in a vertical aspect as a translucent reniform (kidney-shaped) globe." These descriptions are not easy to understand, not from any want of clearness or precision in the words employed, but from the complicated character of the organ, and its very different appearance under different aspects.

To make the matter more intelligible, Mr. Gosse adds, "the structure and action of an apparatus of this type may be made more clear by a homely ill.u.s.tration. Suppose an apple to be divided longitudinally, leaving the stalk attached to one half. Let this now be split again longitudinally so far as the stalk, but not actually separating either portion from it.

Draw the two portions slightly apart, and lay them down on their rounded surfaces. They now represent the quadrantic ma.s.ses in repose, the stalk being the fulcrum, and the upper surfaces being crossed by the teeth. By the contraction of the muscles, of which they are composed, the two segments are made to turn upon their long axis, until the points of the teeth are brought into contact, and the toothed surfaces rise and approach each other. The lower edges do not, however, separate as the upper edges approach, but the form of the ma.s.s alters, becoming more lenticular, so that when the toothed surfaces are brought into their closest approximation, the outline has a subcircular figure. It is on account of this change of form that I presume the ma.s.ses themselves to be partially composed of muscle."

These remarks, although specially made of the _Rotifer macrurus_, are in the main applicable to all the Philodinas, but the student must not expect to understand any of the complicated gizzards of the rotifers without repeated observations, and no small exercise of patience. It is common to call the portions of the Philodine-pattern gizzard "stirrup-shaped," but Mr. Gosse has shown them to be _quadrantic_, that is, shaped like the quarter of a sphere.

As we are not very well off with subjects for description in these two months, we can afford a little time to consider a question that continually arises in the mind, on viewing the movements of animalcules, and especially of any so highly developed as the rotifers, namely, to what extent motions which appear intelligent are really the result of anything like a conscious purpose or will. When any of the lower animals--a bee, for example--acts in precisely the same way as all bees have acted since their proceedings have been observed, we settle the question by the use of the term _instinct_. Those who take the lowest view of insect life, a.s.sume that the bee flies because it has wings, but without wishing to use them, and that the nerves exciting them to action are in their turn excited, not by volition, but by some physical stimulus.

The sight or the smell of flowers is thought by the same reasoners to be capable of attracting the insect, which is unconscious of the attraction, while proximity of food stimulates the tongue to make the movements needful for its acquisition, and so forth. The cells, they tell us, are built according to a pattern which the earliest bee was impelled to construct by forces that bear no a.n.a.logy to human reason and human will, and so originate all the ordinary processes of bee life.

Sometimes, however, it happens that man or accident interposes particular obstacles, and forthwith there appears a particular modification of the orthodox plan, calculated to meet the special difficulty. How is this? Does any one of the difficulties which the bee or the ant is able to get over, produce precisely that kind of electrical disturbance, or polar arrangement of nerve particles that is necessary to stimulate the _first_ step of the action by which the difficulty is surmounted; and does the new condition thus established stimulate the _second_ step, and so forth, or can the bee, within certain limits, really _think_, design, and contrive?

No questions are more difficult of solution; but while protesting against a tendency to undervalue all life below that of man, we must remember we have in our bodies processes going on which are not the result of volition, as when the blood circulates, and its particles arrange themselves in the pattern required to form our tissues and organs, and also that many of our actions belong to the cla.s.s termed by physiologists, "reflex," that is, the result of external impressions upon the nervous system, in which the _sentient_ brain takes no part.

Thus when a strong light stimulates the optic nerve, the portion of brain with which it is connected in its turn stimulates the iris to contract the pupil; and it is supposed that after a man has begun to walk, through the exercise of his will, he may continue to walk, by a reflex action; as his feet press the ground they transmit an impression to the spinal cord, and the legs receive a fresh impulse to locomotion, although the mind is completely occupied with other business, and pays no attention to their proceedings.[14] The ordinary movements of insects appear to be of this character, and to be excited by the ganglia belonging to the segment to which the moving limbs are attached. Thus a centipede will run, after its head has been cut off, and a water-beetle (_Dytiscus_) swam energetically when thrown into water after its brain had been removed.[15]

[14] See Carpenter's 'Manual of Physiology.'

[15] Carpenter's 'Manual of Physiology,' p. 551.

It must not, however, be a.s.sumed that the brain of insects has nothing to do with their movements. It is probably the means of co-ordinating or directing them to a common end, and gives rise to what are called _consensual_ movements, that is, movements which are accompanied or stimulated by a sensation, although not controlled by a will. In man these actions are frequently exhibited, "as when laughter is provoked by some ludicrous sight or sound, or by the remembrance of such at an unseasonable hour."[16] Sneezing is another instance of a sensation leading to certain motions, without any intervention of the human will.

[16] Ibid., p. 543.

Speaking of these consensual motions, Dr. Carpenter observes, "It is probable, from the strong manifestations of emotion, exhibited by many of the lower animals, that some of the actions which we a.s.semble under the general designation of instinctive are to be referred to this group."

The insect brain is composed of a supra-oesophagal ganglion and infra-oesophagal one. Von Siebold says, the first corresponds to the cerebrum of the vertebrata, and "the second is comparable, perhaps, to the cerebellum or spinal cord."[17] The superior ganglion gives off nerves to the antennae and eyes, the lower one to the mandibles, &c. So far as is known the insects that exhibit the most intelligence have the largest and best developed brains.

[17] 'Anatomy of Invertebrates,' Burnett's trans.

A special volume would be required for anything like a complete examination of the little which is known on this subject, but these few remarks may a.s.sist the microscopic beginner in examining the movements of his subjects, and guard against the error of referring to reason and volition those which are, probably, either the direct result of stimulants applied to the surface (as in nerveless creatures), or the indirect (reflex) result of such stimulants in beings like the rotifers, who have a nervous system; or the result of _sensations_, which excite actions without previously referring the matter to the decision of a will. It must not, however, be too readily a.s.sumed that the behaviour of creatures possessing distinct organs is entirely automatic; and we must not forget that even the best physiologists know very little concerning the range of functions which the nervous ganglia of the invertebrata are able to discharge.

CHAPTER VIII.

AUGUST.

Mud coloured by worms--Their retreat at alarm--A country duck-pond--Contents of its sc.u.m--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 cla.s.s 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 a.s.signed to them--and take ourselves once more to our especial subjects.

[Ill.u.s.tration: Cryptomonad--Euglena.]

Knowing that farm-ponds are usually well stocked with microscopic game, we made a dip into one more especially a.s.signed to ducks, and obtained wondrous little for our pains. We were not, however, discouraged, but made an examination of the circ.u.mstances, 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 sc.u.m 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.

[Ill.u.s.tration: 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 a.s.sertion 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 a.s.simulate 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.

[Ill.u.s.tration: Triarthra.]