The Romance of the Microscope / An interesting description of its uses in all branches of science, industry, agriculture, and in the detection of crime, with a short account of its origin, history, and development

by C. A. Ealand

We may come across the young stages of the common gnat. Its eggs are very small and when the mother gnat lays them on the surface of ponds she glues them together so that they form what is known as an “egg raft.” The “raft” we shall notice, if we examine it carefully, is composed of a large number of eggs; each egg is elongated, pointed at one end and blunt at the other. Every egg is arranged with its blunt end downwards for, from that end, the larvæ gnats make their way into the water. A larva, it may be explained, is the stage in insect development which follows the egg; the next stage is known as the pupa. When the eggs are first laid they are white but, before they hatch, they become darker and darker, till they are almost black. The larvæ which hatch from the eggs we must examine under our microscope and also in the water—they may easily be kept in a small jar of pond water. If we study their habits carefully, we shall observe that they float almost at right angles to the surface of the water and that, while doing so, the tip of a little peg-like outgrowth on the tail end of their bodies is thrust out of the water. The little peg is the breathing organ of the gnat larva and the flaps which open and close at its tip are worth examination. In a few days, the denizens of our pond water will change their appearance and become comma shaped. On their heads we shall see a pair of curious horns, which project out of the water as the creatures, which have now become pupæ, float at the surface. The horns are breathing organs. As we examine these pupæ, day by day, we shall see the various parts of the complete gnat as they develop within the body of the comma. Finally, under the microscope, we can trace all the parts of the gnat. Darker and darker the little creatures become, as development proceeds; at the same time they become less active and less comma shaped. At length the time comes when they straighten their tails somewhat violently, their skin splits along the back and out comes the perfect gnat. We can use him for further microscopic work, so we will not let him go. If he be a male, his beautiful feathered feelers or, if a female, her thread-like feelers will make good objects for us, the scales from head and body, the wings and feet are all worth the time we may spend in examining them. The mouth parts, too, are interesting but rather complicated.

Many insects are capable of emitting more or less musical sounds. In some countries these so-called singing insects are kept as pets, in other countries the same insects are voted a nuisance; it is all a matter of taste. Of all musical insects, the most noted is the Cicada and its sound organs are easily seen; they occur only in the male, for the female never sings. The Cicada belongs to the same great order of insects as the green fly, which we have already mentioned. There is one British species, and our readers who visit the New Forest may come upon it. On the under side of one of these insects the beak, very similar to the beak of the green fly, may be plainly seen. On either side of the insect, just below the bases of the wings there are two nearly round discs. These discs cover the sound organs, which are two ear shaped membranes. By means of muscles the insect can cause the membranes to vibrate and thus produce the sound which once heard, can never be forgotten.

More easily found insects, in this country, at any rate, are the cricket and the grasshopper. The cricket we all know is a persistent songster. Let us examine him closely. We shall find, that the house cricket has two pairs of wings; the fore wings are leathery, the hind wings membranous. If we watch a male in the act of chirping, the male crickets like the male Cicadas are the songsters, we shall observe that he moves his wings slightly. If now we examine a dead male, we shall find, on the under surface of the forewing, a rough patch. Let us examine this patch under the microscope, it reminds us of nothing so much as a file: it is a file in fact, and sound is produced by rubbing this rough file against a ridge, which we can easily see, on the upper surface of the hind wing.

It would be a useless accomplishment for the cricket to be able to sing, if there were no ears to hear its song. Nature has arranged that his song shall not go unheard and if we examine a female cricket, that is to say a cricket which has no sound-producing apparatus, we shall find an oval depression, covered by a membrane, on each of her front legs; these are her ears and they enable her to hear her mate calling to her.

We have often heard the song of the grasshopper as we have walked through the fields and he too will occupy our time for a few moments. When he sings, he kicks his legs rather violently and this gives us a clue to the situation of his vocal organs. The inside of each of his hind thighs is ridged and the edge of each ridge is, as we can see if we magnify it, rough like a file. This file-like ridge is rubbed against a smooth ridge on the edge of the fore wing and the result is the familiar note of the grasshopper.

This insect also has ears, but they are not easy to find unless they are pointed out to us. If we examine a grasshopper we shall see that its body is divided into three parts: a head, a solid portion from which the wings and legs arise, the thorax and a portion (the abdomen) made up of a number of rings or segments. On the sides of the first of these rings, counting from the forward end, we shall find small depressions covered with membrane, these are the ears. It is curious that although many of the grasshoppers cannot give out a note, so far as human ears can detect, they nearly all have ears; maybe there is a grasshopper song which only grasshoppers can hear.

Very many other insects have sound organs, but they are nearly all constructed on the same plan. It may seem surprising that sounds can be produced by these simple means. Sound is really caused by waves in the air and these insect vocal organs set up rapid sound waves, by their vibration.

The microscopist should never be at a loss for objects derived from the insect world: it is impossible to walk without treading upon some six legged wayfarer. The wing cases of beetles are often of rare beauty, some on account of their sculpturing, some because of a mantle of scales.

In our greenhouse and garden we can find mealy bugs, curious little powdered insects which do an enormous amount of damage. The fringe wings, or Thrips, are common and destructive; examine their curious feet and their beautifully fringed wings, the sight will repay you. And lastly, if you number an insect enthusiast amongst your friends, enlist his aid in gathering objects for your microscope.