While hunting for our Amœba, it is highly probable that a very active little slipper-shaped organism may have forced himself upon our attention. From his shape he has earned the popular name of the slipper animalcule. He is rather more highly organised than the Amœba for he possesses a mouth, as we shall see when we are able to examine him. So rapidly does he swim, however, that something must be done to curb his activity; he may either be killed with a drop of weak acid or we may put a little tuft of cotton wool on our drop of water and a coverslip lightly over that. The threads of cotton wool will form a network, in the meshes of which the active little animalcule will be confined. Careful observation will show that he is, like a slipper, more pointed at one end than at the other; that there is a funnel-shaped orifice, his mouth, at one side of his body; and that he is covered with little threads which lash the water with rhythmic movement and propel him with considerable rapidity. These little threads also send currents of water to his mouth, and in the water is his food.
Having examined these two free swimming denizens of the pond, we may advantageously turn our attention to some of the weeds growing therein. Careful examination with our pocket lens will almost certainly reveal a number of minute living creatures attached to the submerged stems and leaves. It is impossible to describe all the interesting creatures we might find: we must content ourselves with two, because they are common inhabitants of many ponds. One interesting little creature we are almost certain to find, the Hydra. He may be green or he may be brown but in structure he will remind us of a small sea anemone. When we put him under the microscope he has the appearance of a mass of jelly attached to the water plant on which we found him. He will soon open himself out, however, and we shall see that his free end is provided with a number of tentacles; these he waves about in the water to draw small swimming creatures to his mouth which is situated in the centre of the group of tentacles. Any luckless creature, coming within reach of the Hydra, is at once stung with one of the barb-shaped stings which stud his tentacles and then passed to his mouth. The Hydra is wonderfully tenacious of life; it is said that he has been turned inside out, like a glove finger, without suffering any inconvenience. Probably the specimen we are examining will have a swelling on the side of its body, which might be mistaken for the result of some injury; it is nothing of the kind; it is merely a bud which will grow into a young Hydra and, when old enough, become detached from its parent and float away to another plant. Under a fairly high magnification, we shall almost certainly see something gliding rapidly over the body of the Hydra; its movements are too quick to allow of careful examination; the creature which is almost as elusive as the slipper animalcule is a parasite of the Hydra.
Not quite so common as our last object but still common enough to be mentioned here is the beautiful “bell animalcule.” Like the Hydra, this creature, except in its very young stages, remains affixed to a water plant. In shape the “bell animalcule” resembles a wineglass on a long delicate stem; round the part corresponding to the rim of the glass, there is a fringe of the hair-like, water-lashing structures with which so many of these lowly creatures are provided, and these structures also surround the entrance to the funnel-shaped mouth. When undisturbed, the bell animalcule has its slender stalk fully extended and its little threads lash the water vigorously, causing currents, containing food material, to travel towards its mouth. A sharp tap on the microscope slide will cause the creature to contract, the threads cease their lashing and the stalk contracts spirally, so that the body of the animalcule is drawn close to the object to which it is attached. By degrees the spiral uncoils and the little threads resume their lashing.
Sometimes, as we examine our bell animalcule, we may be fortunate enough to see it splitting into two parts to form two separate individuals. This curious process should be watched carefully. The upper part of the bell splits first and, by degrees the whole bell divides into two equal parts so that we have a pair of bells on a single stalk. The next stage consists of the formation of a ring of whip-like structures round the base of one of the bells; both bells, by the way, have the circlet of whips round their upper edges. Soon after these additional little whips are formed, the owner of them breaks away from the stalk and swims about in the water for a time, finally coming to rest on a suitable water weed. Then the lower ring of whips has served its purpose and in its place a long stalk grows; from this time forward the new bell animalcule will never move from the position it has chosen. This form of increase, this simple splitting takes place over and over again but by degrees the little animal appears to become exhausted and the process slows down or stops.
The partially exhausted Vorticella may gain increased vitality by fusion with another individual and this process also we may have the luck to see though it is less frequent than the simple splitting. Sometimes a bell may be observed to divide, not into halves, but into two unequal parts. The smaller of these parts may divide again into from two to eight parts, each one of which, having developed a fringe of little whips, swims off on its own account. These little barrel-shaped swimming forms, instead of settling down and forming stalked bells, seek an exhausted creature, fuse with it near the base of its bell and finally become absorbed by it. The result of this fusion is that the bell animalcule takes on a new lease of life and once more begins to divide actively.
In our search for specimens for our microscope we may come across a very common pond dweller, closely related to the bell animalcule, known by the name of Carchesium Spectabile. We cannot fail to recognise its family likeness to the form we have already studied, for it consists of a large number of stalked bells growing on a single parent stem. It is really a little colony of bells. When one of the young individuals of Carchesium settles down in the spot it has selected for its dwelling-place, it grows a stalk just as Vorticella did, and it divides later into two individuals. Now in Vorticella only the bell divides, in Carchesium part of the stalk divides also and, instead of swimming away to find a new home it remains attached to the parent stalk. When this has happened several times a goodly colony is formed.
There are few fresh-water animals more commonplace and apparently uninteresting when observed casually than the pond sponge and the river sponge. Yet, if we take either of them home and examine them with the aid of our microscope, we shall be delighted with our specimens. In reality they are of absorbing interest and, at certain times of the year we may easily obtain young sponges, and capital objects they make for the microscope.
Photos by Flatters & Garnett
1. Starch Grains of Potato