CHAPTER XV
THE MICROSCOPE BY THE SEASIDE—ANIMAL LIFE

It is always surprising that the majority of microscopists never dream of examining any of the hundreds of beautiful objects which can be found by the seaside, in the course of an afternoon’s ramble. That every pond will contain ample material for study, the microscopist knows instinctively; insect life and plant life also he studies, but the microscope is generally left at home when a visit is paid to the seaside. A rocky coast is better than a sandy one, for rock pools yield many objects, and the warmer southern waters of our coasts are better than the colder northern seas, but the microscopist who finds himself on a northern sandy coast need not despair, if he search diligently he will find material enough to occupy him for many a day.

Nearly every rock pool will provide one or more Sea Anemones; it is hardly necessary to describe these “flowers of the sea” as they have been called, they are such familiar objects and the brilliant colouring of some of them makes them highly attractive. In many respects Sea Anemones resemble the Hydra, one of the pond dwellers, they are rather more highly developed, however. Any Sea Anemone will serve our purpose because we are about to examine the little darts with which its tentacles, and even its body, are armed. If we find several different kinds of Anemone, we must take the most transparent we can find and also a small specimen; we can examine the larger, more opaque ones later. Having transferred our specimen to a small jar, containing but a small quantity of sea water, we wait till it has recovered from its transfer and spread its tentacles, then it must be killed by one of the methods suggested in our concluding chapter (see p. 306). One of the tentacles must then be snipped off with scissors—some people cut off the tentacle without killing the Anemone and the animal does not appear to suffer a great amount of inconvenience, in fact a new tentacle soon grows to take the place of the old one. We do not recommend promiscuous vivisection. The tentacle is placed on a clean slide, a cover slip placed over it and pressure is applied. An enormous number of little thread-like darts are pressed from all parts of the tentacle. In some cases, little oval capsules are squeezed out and, in the capsules, the darts may be plainly seen, coiled up. On applying pressure to a capsule, the contained dart will shoot forth, much as does a glove finger turned inside out, when we blow violently into the glove. These little darts are of the greatest interest to the microscopist; they vary in shape according to the kind of Anemone, as we shall find if we try this experiment with various Anemones. Some of them are straight with stiff bristles at their bases; some have backwardly directed barbs at their tips; others are apparently jointed, forming a zigzag, with a short length of the dart going from left to right, the next short length from right to left, and so on to the tip. It is marvellous how the darts can be accommodated within the capsule, for the average length of the latter is but 1/300 inch whereas its dart may measure 1/8 inch. These little threads contain a poison capable of paralyzing any moderate-sized fishes which they touch.

Have you ever seen a “comb bearer” or as it is often called, a “marble bleb?” Probably you have though you may not know its name. Sometimes it occurs in rock pools, though more often it is found in one’s shrimping net and occasionally it is washed up by the tide, but it does not live long out of water. The “marble bleb,” as its name denotes, is an almost globular mass of soft, transparent jelly. It is practically colourless, with the exception of eight bright coloured bands which run from end to end of the animal. To the naked eye, this little denizen of the sea is of rare beauty: as an object for low-power microscopy it is entrancing.

When magnified, the bright bands are seen to be composed of rows of flattened outgrowths. If our specimen is small enough to be examined in water, its real beauty can only be seen in this manner, we shall observe that the flattened outgrowths act like paddles, sometimes they work all together, sometimes independently of one another and this fact explains the marvellous evolutions of the “marble bleb” in water. Now it shoots forward in a straight line with some rapidity, now it rolls over and over and swims onward while doing so.

In the sun, it displays glorious iridescent colouring. At the hinder end of the “bleb” we notice a pair of hollows: from these, as we watch it swim, we shall see it suddenly shoot out a pair of long feathery tendrils and they may be withdrawn into the hollows as suddenly. We must make a point of examining the “marble bleb,” it is one of the gems of our coasts.

Superficially the common, sponge-like “Dead man’s toes” or, to give it its more pleasant title, “Mermaid’s fingers,” is a very drab affair. It is a dirty-brown lobed, spongy mass with a leathery skin; when removed from the water it loses all semblance of shape. In sea water, however, if we examine it carefully, we shall see that it is studded with beautiful little flower-like creatures, each one resembling a miniature Sea Anemone. Examined, in water, under a low power of our microscope we can see the water current flowing through the channels with which it is perforated, after the manner of a sponge. If, now, we take a dead specimen and cut it up, placing a small portion on a slide and shredding it with a pair of needles, we shall find, when we magnify the result of our work, that there are a number of minute mineral spikes, called spicules, and very beautiful objects they make for the microscope. There are many sea-side creatures, which we may find, closely related to “Mermaid’s fingers,” they may all be treated in the same way for they will all yield spicules which will repay us for our trouble. All these spongy organisms are not provided with spicules as ornaments, though one might be forgiven for thinking so, seeing how decorative many of them are. Their presence is necessary to strengthen the spongy material.

The specimen we have just examined is not one animal but a colony of very minute animals. These colonies are very common, not only in salt but also in fresh water. They serve a useful purpose, for the creatures composing them are so minute that they would fare badly did they dwell alone. Dwelling together as they do and each one contributing its share to the building of the home they appear to thrive to a wonderful degree. The coral islands are built, as to their foundations at anyrate, by millions of very minute animals, living together in colonies.

We mentioned the sponges a moment ago and many of them may be found around our coasts; not the household sponges we know so well, but much smaller, though equally interesting, colonies. Like the better known sponges, those which we find on our shores are perforated with a number of holes through which the water is driven by means of little whip-like structures which line the cavities. Professor Grant has graphically described his impressions at witnessing this water current for the first time. “I put a small branch of the Spongia Coalita,” he writes, “with some sea water in a watch glass, under the microscope, and, on reflecting the light of a candle up through the fluid, I soon perceived that there was some internal motion in the opaque particles floating through the water. On moving the watch glass, so as to bring one of the apertures on the side of the sponge fully into view, I beheld, for the first time, the splendid spectacle of this living fountain vomiting forth from a circular cavity an impetuous torrent of liquid matter, and hurling along, in rapid succession, opaque masses, which it strewed everywhere around. The beauty and novelty of such a scene in the Animal Kingdom long arrested my attention; but after twenty-five minutes of constant observation, I was obliged to withdraw my eye from fatigue, without having seen the torrent for one instant change its direction, or diminish, in the slightest degree, the rapidity of its course. I continued to watch the same orifice, at short intervals, for five hours, sometimes observing it for a quarter of an hour at a time, but still the stream rolled on with a constant and even velocity. About the end of this time, however, I observed the current to become perceptibly languid ... and in one hour more the current had entirely ceased.”

Frequently the sponge we examine may be found to be studded with many yellowish spots; closer examination will show that these spots are composed of very small jelly covered eggs. Later these eggs find their way into the cavities of the sponge and are forced therefrom in the currents of water. Each of the young sponges thus expelled is furnished with a covering of little whips, by means of which it swims about till it can find a suitable spot on which to anchor and complete its growth.

The Sea Anemone, which has already provided us with objects for our microscope, has many near relatives which we must make a point of examining, while we have the opportunity. Many of these creatures, or rather their colonies, for they do not live singly, are to the naked eye, strangely like seaweeds. A number of them are moss-like and may be found on wooden breakwaters and similar situations when the tide is low; they should be collected and examined and, to see them at their best they should be examined under water. It is hardly necessary to describe any one of these colonies in detail, for they are so numerous that the one we described might not come into the hands of our readers for a long time. In general characters they are all somewhat similar so we will confine ourselves to generalities. For the most part, the stems and branches of these colonies are of the thickness of thread. As we watch them under the microscope we shall see that they are studded with little cups and, presently, from each little cup there appears a little tuft of tentacles which is waved about in the water. Each member of the colony is similar to its neighbour and each one, again, is very like the fresh water Hydra with which we are familiar.

Of all the common objects of the sea shore one of the commonest everywhere is the sea-mat. Nine people out of ten or, we might safely say that everyone who had not learned its true nature, would guess it to be a seaweed. As we find it washed up on the beach it is almost the colour of sand, somewhat rough to the touch, whilst its whole surface is pitted with minute holes. The sea-mat, when dry as we usually find it, is a remnant of a colony of sea dwellers very similar to those we have just described. From each little hole, in a living specimen, which we can find without much difficulty, there appear the familiar tentacles; each hole is the home of a minute hydra-like animal.

Hooke, whom we mentioned in our chapter on the History of the Microscope, though a careful observer, was quite misled by the sea-mat; he thought it was a seaweed, for he wrote: “I have not, among all plants and vegetables I have yet observed, seen any one comparable to this seaweed. It is a plant which grows upon the rocks under water and increases and spreads itself into a great tuft, which is not only handsomely branched into several leaves, but the whole surface is covered over with a most curious knot of carved work, which consists of a texture much resembling a honeycomb, for the whole surface on both sides is covered over with a multitude of very small holes, being no larger than so many holes made with a pin, and ranged in the neatest and most delicate order imaginable, they being placed in the manner of a quincunx, or very much like the rows of eyes of a fly, the rows or orders being very regular which way soever they are observed. These little holes, which to the eye look round, when magnified, appear very regularly shaped holes, representing almost the shape of a round-toed shoe, the hinder part of each being, as it were, turned in, or covered by the toe of the next below it. These holes seemed walled about with very thin and transparent substance, looking of a pale straw colour, from the edge of which, against the middle of each hole, were sprouted out four small, transparent, straw-coloured thorns, which seemed to protect and cover those cavities.”

As a well-known author has remarked: “This is really a wonderfully faithful description of the common sea-mat, and one cannot help picturing the surprise and delight of old author Hooke, could he have seen a portion of a living colony under a modern microscope.”

One of our finds may be the “Bird’s head.” It is a branched form, quite unlike the sea-mat but it is of even greater interest. Under the microscope, we shall see the many waving tentacles, but another feature is sure to attract our attention, a feature which is responsible for the popular name of the colony. On the outside of each cavity containing a member of the colony there is a structure which resembles nothing so much as a hawk-like bird’s head atop of a long neck. While the tentacles wave in the water, the bird’s head snaps vigorously, moved here and moved there. The birds’ heads, which might be mistaken for parasites stealing food from the waving tentacles, really perform the useful function of keeping them clean and warding off creatures which might do them harm.

Now let us pass to quite different though equally common sea shore animals, the star fish. There are very many kinds but the common star fish will serve our purpose well. We may make a beginning by examining his back under a low magnification and observing that it is protected by a number of hard plates which form a very efficient armour. At the point where two of the rays (the finger like structures) arise we shall notice a small flat plate, this too is worth a moment’s inspection, for it is the water pore through which the star fish takes in water.

The under surface of the star fish shows us of course its mouth in the centre of its body, the soft fleshy suckers which cover the rays, with the exception of a narrow line down the centre of each one. At the tip of each ray there is an eye; it may easily be distinguished by its bright red colour and microscopic examination will show us that it is quite unlike any of the other eyes we have examined. Over each eye there is a little tentacle; these little tentacles may be called the noses of the star fish, for, by means of them it is able to smell. They are as unlike our idea of a nose as are the little pits on the feeler of the cockchafer which we examined, yet these noses and ours all perform the same duties. Our time will be well spent if we devote some of it to a search for others less common star fish. Some of them are really beautiful and whatever specimens we come across can be compared with the common variety which is everywhere.

Closely related to the star fish are the sea-urchins. The relationship may not be apparent at first sight but a careful study of an urchin and a star will reveal many points of similarity. Our object in these pages, however, is to find material for our microscope and not to unfold the relationships of various members of the Animal Kingdom. When we have learned to cut sections, we may try our hand at the spine of a sea-urchin, it is an object well worthy of study. The hard shell of the urchin may be examined under a low magnification, we shall see then that his armour is far more highly developed than that of the star fish.

Another near relative of the two animals we have just described is the sea slug or sea cucumber. Though an article of commerce of some importance in the far East, the sea slug is not so common on our coasts as its relations. We must make a point of finding a specimen, however, for it provides us with one of the most remarkable objects for our microscope that could possibly be imagined. One species, which goes by the name of Synapta Inhærens, is the one most worthy of examination. We must describe the creature first of all so that we may know what to look for. It is aptly named sea cucumber for it is not unlike that fruit—yes! fruit is correct, though the cucumber is more often called a vegetable. The animal’s skin is tough and leathery and at the head end there is a fringe of feathery tentacles. The sea cucumber must be looked for amongst sea weeds or, maybe, he lies buried in the sand, with only his fringe of tentacles on view. A friendly fisherman will probably aid us in our search.

Having found our creature we must examine his leathery skin under the microscope. To the touch it is evident that it is studded with some flinty matter, but the microscope alone can show us the amazing beauty of this armour. Under a low magnification, we can see, dotted over the leathery skin, some nearly circular plates to each of which is attached a little anchor. Now, from a dead animal of course, we must scrape away some of these objects and examine them with a higher magnification. Even the hardened microscopist will be delighted when he sees the armour of the sea cucumber for the first time. Each anchor is hinged to a little plate, each little plate, nearly circular in outline, is perforated with seven holes, six round the circumference and one in the centre and every perforation has a toothed margin. So perfect are these minute plates and anchors, that the most intricate man-made machinery could not have turned them out more perfectly to pattern. They are precisely similar to one another in size and shape; as objects for the microscope, even the sea with all its store of wonders, can offer us nothing more marvellous.

We may number the sea mouse amongst our treasures of the sea-side. Though called a mouse, on account of its curious movements and partly perhaps because of its appearance, it is really a worm. It does not appear to have the slightest resemblance to the common earth worm, nor to the liver fluke which is described on another page, nevertheless, it is related to both these creatures. The raiment of the sea mouse is gorgeous in the extreme; on its back is soft brownish hair, its sides are clothed with yellow and green hair, displaying a wonderful iridescence and amongst the hair on the sides there are many stiff brown bristles. Of the covering of the sea mouse it has been said: “It is as if all the hues of the rainbow were collected there, making this remarkable animal a living jewel, and truly worthy of the name of Aphrodite, the Queen of Beauty.” The bristles of this creature we must examine microscopically, they vary in structure according to the kind of sea mouse, for there are several kinds, but in some of them they are formidably barbed, in all of them they act as a protection.

Many other worms, a number of them un-wormlike in appearance will claim our attention but we cannot devote more space to them here. There is the common shell-binder, a curious worm, which builds for itself a still more curious shelter of broken shells. Another worm, Serpula by name, also lives in tube-like structures of its own manufacture and is remarkable in that a row of nearly two thousand seven-toothed hooks run along its back and all these thirteen thousand odd teeth are there merely for the purpose of holding Serpula in its tubular home.

Much interesting work may be done at the seaside in studying the young stages of various familiar creatures. This work, however, necessitates the keeping of the adults in an aquarium; for the young ones, in most cases, are so unlike their parents that, if found swimming about on their own account, they would never be recognised. Young barnacles, for instance, have six legs, a tubular mouth and a single eye. At a later stage they might be mistaken for young shell fish; they possess a shell, not unlike that of the mussel, containing, however, not a soft, fleshy mollusc but a six legged creature which swims through the water in jerks, after the manner of a water flea. Strangely enough, it is now provided with two stalked eyes like those of a crab, whilst of mouth parts it has none, or they are so imperfectly developed as to be useless for feeding. Soon this active youngster settles down for the rest of its life and becomes a sedate and sedentary barnacle, with one imperfectly developed eye and a mouth capable of feeding to good purpose.

Young crabs are equally curious and also totally unlike their parents, but these curious creatures are hardly accessible to those who only pay a flying visit to the sea-side. As we have remarked, an aquarium is a necessity and to keep marine animals inland is a feat beyond the powers of the ordinary mortal.

The Sea Lemon or Doris is a curious little creature, worthy of examination. Its habit is to feed upon sponges and strange diet it is, for we remember that all sponges are fortified with hard flinty structures, called spicules. This habit of the Sea Lemon is of use to the microscopist, for the stomach of the creature is always laden with the indigestible spicules and a very interesting collection of these beautiful structures may be gathered together in this manner. The egg masses of Doris may be looked for on rocks during the summer. Enormous numbers of eggs are laid in a jelly-like mass. Some of this jelly may be collected and examined under the microscope and, should we have collected our material at a favourable moment, we may watch the eggs hatch and observe the young Sea Lemons in their delicate transparent shells swimming round and round the chamber within which they are imprisoned during the very early stages of their lives.

Very frequently in the summer, when the seas are warm any agitation of the water causes a beautiful phosphorescence to appear. Phosphorescence, by the way, may be described as light without heat and it is not uncommon in nature. Glow worms and fireflies are phosphorescent; fish, also, in the dead state, often emit a certain amount of light as do bones whilst, of course, phosphorous itself is the best example of a naturally phosphorescent body. Phosphorescent sea water, however, owes its peculiarity to myriads of minute animals and they will afford us an interesting half hour with the microscope. Let us collect a little of this water in a glass jar and take it into a darkened room that we may the better see the phosphorescence. When the water in the jar is undisturbed, we can see nothing unusual; if we stir it or strike it a faint greenish light is given off, but it does not last for long. Now, on taking the jar into the daylight, as soon as our eyes are accustomed to the light, we shall just be able to see that there are some very small living creatures on the surface of the water. We must examine one, under a fairly high magnification; it may be transferred, from the jar to a drop of water on our slide, by means of a paint brush. The little animal which is responsible for the phosphorescence of sea water is strangely reminiscent of an apple with its stalk. It is, of course, very minute being only 1/60 inch in diameter and its tail, which we have compared to the stalk of the apple, is equal to the diameter in length. The whole creature is quite transparent. As we watch it swim in our drop of water, we shall notice that it propels itself by the lashing of its tail.

There are countless animals of the sea we have not so much as mentioned, but the marine gardens contain plants so interesting and so totally unlike those which live upon land that we must devote a few pages to them also.

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