examined, it will be seen that the body is made up of segments or rings, and that it moves by successively shortening and elongating its body. Extending through the middle of the body is an alimentary canal con- sisting of a mouth, gizzard for grinding food, stomach and intestines.
Near the head is a little nerve center. The whole animal may be regarded as built up by the joining of a number of essentially similar segments. A more minute examination will show that these segments have been materially modified in some portions of the animal, but they have not been in any respect organized, as have the different parts of higher animals. This simple animal, as has already been seen, is an untiring worker in preparing and fertilizing soil for plants, and thus is a most efficient helper to man.
104.Insects.
Experiment 114. -Procure a grasshopper or honeybee, as a type insect, and inclose it in a small glass-covered box. Into how many parts is the bodydivided? Describe these parts. To which part are the legs attached? The wings? How many legs are there? How many wings? Notice the largest part into which the body is divided. Notice the eyes and the feelers, or antenn?, on the head. Write a short description of the general characteristics of the bee"s body.
This class contains more than half the known animal species. They are spread widely over all parts of the earth.
Both good and bad insects abound. Economically, they furnish millions upon millions of dollars worth of produce every year and on the other hand destroy hundreds of millions of dollars worth of crops and trees. It has been estimated that in the United States insects destroy every year crops and trees which have a value of $50,000,000, to say nothing of the countless losses due to diseases spread byflies and mosquitoes. Not many years ago
grasshoppers nearly devastated several of the middle western states.
BUTTERFLIES ON ALFALFA.
Fig. 107.
The most productive insects are the silk worms and the bees. Without the silk worm (Fig. 107) there would be no silk produced, and without the bee, no honey. These two products each year run into hundreds of millions of dollars. We have already seen that bees and other insectsare needed also for the fertilization of flowers.
Among the most interesting of the insects and perhaps, everything considered, the most valuable, is the honey-bee. This is the great flower fertilizer; it would fertilize about all the plants man really needs except the red clover. In the United States alone there is produced by it about twenty-five million dollars worth of honey and wax each year.
In Experiment 114, it was found that the body of the bee, like other insects, is divided into three parts. These parts are called head, thorax and abdomen. The eyes and the feelers, or antenn?, are on the head. The mouth is a very complex organ, fitted both for biting and for sucking. The six legs and four wings are on the thorax. The hind leg of each working bee is so shaped and fringed with hairs that it forms a pollen basket.
Honey-bees live in large colonies and in the colony there are three kinds of bees, the male bees, or drones, the workers and the queen or female bee. The workers are the ones that make all of the honey and wax, do all the work of the hive and feed the grubs on rich food formed in their own stomachs, as well as on pollen mixed with honey. The grubs are the first stage in the development of the bee from the egg. The queen lays all the eggs, sometimes as many as a million. There is but one queen in each swarm. Whenever another queen is ready to be hatched, the old queen takes about half the colony and goes off to form another swarm.
The wax is secreted from glands in the abdomen of the workers and with this the bees build the comb. Each cell is hexagonal in cross section and the comb is so constructed that the least possible amountBEEHIVES.
Hundreds of dollars worth of honey are produced here each year.
of wax will inclose the greatest possible amount of honey. The nectar at the bases of flowers supplies the bee with the material from which it makes the honey. It is in seeking for this that the bee visits so many flowers and scrapes the pollen on to the different parts of its body to be borne away to fertilize other flowers which it enters. Such an interesting animal and so exceedingly useful is the bee that hundreds of books have been written about it, more than about any other domestic animal. Some of these should be read for further information concerning this most instructive animal.
105.Vertebrates.
Experiment 115. -If possible, secure the skeleton of some vertebrate animal, preferably man. Notice how the bones are fitted to each other and how the joints are arranged to allow movement. Observe how carefully the brain and the spinal cord are protected, and also the thorax, which contains the heart and lungs. If a human skeleton is procured, notice the curving of the spine which enables the body to stand erect.
A HUMAN SKELETON.
Notice how the bones are arranged to protect the delicate organs.
We have just studied briefly some of the invertebrates most closely related to the welfare or injury of man. Man himself belongs to the other great class, vertebrates. The higher animals which furnish him with the greater part of his animal food also belong to this class. Although there are great variations in the structure of vertebrate animals, yet they are alike in having a backbone and an inner supporting skeleton.
The bony skeleton in the higher forms of animallife consists of a vertebral column, skull, ribs and appendages. The main skeleton protects the most delicate organs and acts as a support for the attachment of the muscles. The appendages, like the legs and arms in man, are jointed to the central part of the skeleton, and it is the action of the muscles in moving these about the joints that makes movement from place to place possible.