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.