Earthworms can breathe only when the surfaces of their bodies are in moist conditions.
Go out at night with a lantern to where earthworms are known to have burrows, observe the worms stretched out with the rear ends of their bodies attached to the burrows, and note how quickly they draw back when they are touched. Do they draw back if the ground is jarred near them?
Do they draw back when the light falls upon them?
State the facts which are taught by the observations which were made on the above topics.
CLa.s.s-ROOM LESSON
Put two or three earthworms into a jar of rich, damp soil, on top of which there is a layer of sand a quarter of an inch thick. Put bits of cabbage, onion, gra.s.s, and other plants on the surface and cover the jar with a gla.s.s slip or cardboard.
After a few days, examine the jar, noting the number of burrows, the foods selected, the castings, the food dragged into the burrows. Pour water into the jar and observe the actions of the worms. Can an earthworm live in water?
Place an earthworm on a moist plate or board and direct the pupils to study it, as follows:
Distinguish the head from the rear end, the upper from the lower surface. Observe the means of living. To a.s.sist in the latter observation, stroke the worm from rear to head and find the four double rows of bristles. Why is it difficult to pull an earthworm out of its burrow?
Find the mouth. Has the earthworm any eyes, ears, or nose? Place a pin in the path of a moving worm and try to explain why it turns aside before touching the obstacle. Test the sensitiveness to feeling. Why is it cruel to put an earthworm on a fishhook?
From the soil castings found in the jar, infer the value of earthworms for enriching and pulverizing soil. (See "Soil Studies", p. 269.)
REFERENCES
Bailey and Coleman: _First Course in Biology._ Macmillan Co. $1.25.
Crawford: _Guide to Nature Study._ The Copp, Clark Co. 90 cents.
Kellogg: _Elementary Zoology._ Holt & Co. $1.35.
THE AQUARIUM
A large gla.s.s aquarium may be purchased from any School Supply Company at a cost of a few dollars, but a small globe-shaped aquarium such as is used for gold-fishes will be found suitable for school purposes. If it is not possible to secure either of these, a large gla.s.s jar, such as a battery jar or large fruit jar, will be found to answer quite well.
To set up the aquarium, put into the jar about two inches of clean sh.o.r.e sand (sand from a sand pit, washed until the water comes away clear, will do). Secure from a pond some water-plants, place these in the jar with their roots covered with sand and secured in position by small stones. Pour in water until the jar is nearly full, taking care not to wash the roots out of place, and then put in a freshwater clam and a few water snails. These are scavengers, for the clam feeds upon organisms that float in the water, while the snails eat the green sc.u.m that grows on the gla.s.s.
The other aquarium specimens may now be put in. One fish about three inches long to a gallon of water is about the right proportion. When there is a sufficient quant.i.ty of plant life to keep the water properly oxygenated and enough animal life to supply the carbon dioxide necessary to keep the plants growing well, the aquarium is said to be _balanced_.
The balanced aquarium does not require that the water be changed more often than once in two months.
Too much direct sunlight causes too rapid growth of green slime, hence the aquarium should not be set in a window. Close to a window through which the sun shines upon it for an hour or longer each day is the best position.
Do not supply more food to the animals in the aquarium than they can eat up clean.
Crayfish, perch, trout, and other freshwater fishes are destructive of insect larvae and other aquarium specimens, hence care must be taken in selecting the specimens that are put together into an aquarium.
Suitable animals for the aquarium: mosquito larvae, dragon-fly larvae, caddice-fly larvae, crayfish, clam, water snails, tadpoles, fish, frog, turtle.
AQUARIUM SPECIMENS
MOSQUITO
Time.--May or June.
~Questions and Observations.~--At what time of the year are mosquitoes most plentiful? In what localities are they most plentiful? Why are they most plentiful in these places? Are mosquitoes ever seen during fall or winter? How do you account for their rapid increase in number early in summer?
How do mosquitoes find their victims? Observe the humming noise and try to discover how it is made.
Watch a mosquito as it draws blood from your hand. Does the point of the beak pierce the skin?
Capture a number of mosquitoes and place them in a jar containing some water and a few straws or sticks standing upright out of the water.
Cover the mouth of the jar with a gla.s.s plate or fine gauze. Watch for the rafts of mosquitoes" eggs on the surface of the water.
The eggs may also be found on the surface of ponds or open rain barrels, and may be transferred to water in a jar in the laboratory.
STUDY OF THE ADULT FORM
Note the shape, colour, sucking tube, wings, and legs. Compare with the house-fly.
Distinguish the male insect from the female; the former has feathery feelers, and has mouth parts unsuited for biting.
How many kinds of mosquitoes have you seen? Direct attention to the kind which causes the spread of malaria. It is recognized by its habit of standing with its body pointing at right angles to the surface on which its feet are placed or, in other words, it appears to stand on its head.
THE DEVELOPMENT
Describe the egg raft.
Observe the wigglers (hatched in about a day); the divisions of the body of the wigglers; position of the wigglers when at rest. Observe that the tail end is upward. Lead the pupils to perceive that this is the means of getting air.
Observe the rapid movement toward the bottom when disturbed; the means of causing this movement; the change into the large-headed pupae--a change which takes place about ten days after hatching; the almost motionless character of the pupae; the change from the pupae forms into the adult--a change which takes place at about the fourth day of pupae life.
Put some mosquito larvae (wigglers) into the fish aquarium. Are mosquitoes of any use? The wigglers are the food on which some young fishes live. Young ba.s.s and trout feed upon them.
Put some kerosene on the surface of a jar in which there are mosquito larvae. Describe a method of destroying mosquitoes.
The teacher tells about the mosquito as the cause of the spread of malaria. From the fact that the eggs hatch on stagnant water, deduce a benefit arising from the draining of land.
REFERENCES
Silc.o.x and Stevenson: _Modern Nature Study_
Hodge: _Nature Study and Life_
CADDICE-FLY
Time: May.
The caddice-flies are very interesting insects, owing to the habits of the larvae of building little cases of wood, stones, or sh.e.l.ls, in which they pa.s.s their development stages under water.