In case the name of the insect is not known to you, use a number and some designation as to color or other mark by which it may be known until you have leisure to look up its name by means of keys or books on insects.

Special Field Studies

The questions below may be used for a more careful field study of any insect.

1. Just where was the insect found?
2. Note carefully what the insects are doing before they are disturbed by your presence. What did the insects do when you disturbed them? If you think this related to securing safety, explain what leads you to think so.
3. What senses do you conclude are well developed? Reason for your conclusion.
4. Has the insect a home? If so, what is its character?
5. What is the color? What is the relation between the color of the insect and its surroundings?
6. Is the insect solitary in its habits or associated with others of the same species? If in association with others, note the numbers, and what they are doing.
7. What modes of locomotion do you observe in this insect? Which is the most common? If it flies or jumps, note the distance.
8. If you find the young, note whether they differ from the adult in general appearance, and if so, in what ways they differ. Do they differ in food?
9. What other insects do you find in the same habitat?

2. A STUDY OF GRASSHOPPERS (LOCUSTS)

Definitions.

Orthoptera,

straight-winged insects, order to which belong grasshoppers, locusts, katydids, crickets, cockroaches, etc.

Vivarium,

a cage in which living animals are kept.

Anterior,

toward the head of an animal.

Posterior,

opposite to anterior.

Dorsal,

the upper surface of an animal.

Ventral,

opposite to dorsal.

Regions,

principal divisions of the body of an animal.

Head, thorax, and abdomen,

the three distinct regions into which the body of a grasshopper is divided.

Somite,

a ring-like division of the body of an animal.

Prothorax, mesothorax, and metathorax,

the three divisions or somites into which the thorax of any insect is divided. A pair of legs is borne on each division.

Exoskeleton,

an external skeleton.

Femur, tibia, and tarsus,

the three principal divisions of the leg corresponding to thigh, shank, and foot.

Veins,

thread-like thickenings of the wings.

Ocelli,

the single or simple eyes of an insect, composed of a single eye element.

Compound eyes,

made up of many eye elements.

Auditory sacs,

organs for hearing in many animals.

Antennæ,

the feelers borne on the head.

Labrum,

the upper lip.

Labium,

the lower lip, formed by the growing together of the second maxillæ.

Mandibles,

primary jaws situated under the labrum.

Maxillæ,

secondary jaws just in front of the labium, each composed of three parts, a palp, a spoon, and a tooth.

Palps,

the jointed finger-like structures used to handle food, one pair on the labium and one pair on the maxillæ.

Spiracles,

openings into the trachea found along the sides of the abdomen and thorax.

Tracheæ,

slender tubes used for breathing organs among insects. They carry the air direct to the tissues in all parts of the body.

Ovipositors,

structures on the posterior end of the abdomen of a female, used to deposit eggs.

Metamorphosis,

refers to the development of the young of animals when striking changes in structure occur in the course of their growth. Metamorphosis is called complete when the young have no resemblance to the adults, and incomplete when there is a resemblance to the adult. In complete metamorphosis the stages are larva, pupa, and adult. In incomplete metamorphosis the stages are nymph and adult.

Observations.

The Body.

1. Show how the shape of the grasshopper's body is well adapted to its needs.
2. Which region of the body is the thickest? What seems to be the reason for this? Which regions are capable of movement?

Locomotion.

1. What are the various kinds of locomotion a grasshopper can use? Which are used in the vivarium and which when free in the laboratory?
2. Which legs are used in jumping? How are these legs especially adapted to this, in length, structure and direction? Could a grasshopper jump if the third pair of legs were arranged like the other two pairs? Why?
3. How is the animal able to cling to grass stems and not slip down? What is the direction of the body in relation to the stem or grass blade?
4. What is the position of the wings when at rest? when in use? How do the hind wings fold? How are the principal veins of the wings arranged to permit or facilitate this folding?
5. Contrast the fore and hind wings with respect to thickness, size, and use.
6. To which somites of the thorax are the wings attached? Nearer which surface, the dorsal or ventral? Why?

Sense Organs.

1. Discover all you can about the uses of the antennæ by carefully observing grasshoppers at rest, feeding, jumping and crawling, approaching an object or another grasshopper, etc.
2. How many compound eyes has the grasshopper? How many simple eyes? Where are they located?

   Examine a preparation of the compound eye with the low power or as demonstrated with the stereopticon. What is the shape of an eye element of the compound eye? About how many eye elements are there in a compound eye?

Feeding.

1. Do grasshoppers eat and drink while in captivity? Put a fresh bunch of grass which has been sprinkled with water in a vivarium with grasshoppers that have had no food or drink for twenty-four hours and watch results.
2. What is the position of the grasshoppers in feeding? In what direction do the jaws move in feeding? Compare this with the direction of movement of your own jaws. What is the use of the palps? What do you think is the use of the "molasses" or saliva that flows from the mouth?

Respiration.

1. Describe the breathing movements of a grasshopper and explain the relation of the movements to inhalation and exhalation of air.
2. Find the exact location and number of spiracles on the abdomen. There are two pairs of spiracles on the thorax. Find them. How do the spiracles prevent the entrance of dust?

   Describe a trachea as seen in a mounted preparation with the aid of a microscope or stereopticon.

Protection.

1. Explain how the colors of the grasshopper may be protective or useful when at rest in its natural habitat and when in flight.
2. Does the shell cover the entire body? What are the advantages of such a covering? A shell is likely to hinder activity, sensitiveness, and growth. How are such disadvantages overcome in this case?
3. What senses are probably most relied upon to detect approaching danger? Give evidence to support your answer.
4. What is the position of the hind legs when at rest? What relation has this to safety?

Reproduction and Development.

1. Describe the ovipositors and the probable method of their use. Describe the egg packets of grasshoppers, if discovered. About how many eggs in one? (They are sometimes seen against the glass sides of the vivaria.)
2. If you have young grasshoppers of various ages, arrange a set of them in what seems to you to be the order of their development. How do young grasshoppers differ from adults? What changes take place as they develop? What kind of metamorphosis is this?

Summary of Important Points in the Study of the Grasshopper

1. How many and what distinct regions of the body are there?
2. How many antennæ? Compare their length with that of the body. What other sense organs did you discover?
3. How many legs? For what specially adapted? How?
4. How many wings? What is their resting position? How do the fore wings differ from the hind wings? How do the hind wings fold?
5. To what kind of feeding are they adapted, biting or sucking the food? How many and what sets of mouth parts are there?
6. How is air necessary for respiration obtained?
7. In what various ways are grasshoppers fitted for life in meadows and weed plots?
8. How do they meet winter conditions?
9. What kind of metamorphosis has the grasshopper?

Drawings suggested.

1. Side view with the legs and wings removed. Label all parts shown in this drawing. (See Definitions on pages 23 and 24 for names of parts.)
2. Face view of the head, showing the simple and compound eyes, the antennæ, labrum, and palps.
3. One of the third pair of legs. Label parts.
4. A fore and a hind wing arranged in natural position.
5. A young grasshopper.

3. COMPARATIVE STUDY OF ORTHOPTERA

4. KEY TO SOME COMMON ORTHOPTERA

5. THE DRAGON FLY

6. THE HONEYBEE

The Worker Bee.

1. Observe and describe the form, size, regions, and covering of the bee. What are its colors?
2. Observe and describe the texture, veining, relative size, and position of the wings. Discover how the fore and hind wings are hooked together. What advantage in having them hooked together?
3. For what kind of locomotion are the legs best adapted?
4. Find the pollen basket on the tarsus of a hind leg. How is it fitted for carrying pollen? What are the wax shears?
   1. Examine and describe the structure at the posterior end of the body used for stinging. (Use a mounted preparation for this with low-power of microscope.)
   2. The mouth parts are fitted for both biting and sucking. Find what makes this possible. (Use mounted preparation.)
5. Describe the antennæ and the number, position, and shape of the eyes. Are the eyes fitted for keen sight? Give reason for answer.
6. The worker bee gathers honey and pollen and defends the entire community from enemies. What various adaptations fit it for this work?

The Community of Bees.

1. How do the workers, drones, and queen differ in general appearance?
2. Describe the appearance of the comb and the arrangement and shape of the cells. Why this shape? How are the cells closed when full of honey?
3. How do the cells used for rearing worker bees differ from those used for rearing queens? What is the appearance of the larvæ? Of the pupa?
4. Examine and test in various ways a small piece of beeswax. What are the qualities possessed by this wax which make it suitable for making comb and protecting the home from storms?

Supplementary Studies of Bees

Materials.

For this study an observation hive of bees or opportunity to visit an apiary will be helpful. If neither are practicable, then look up the answers in books. There are government bulletins on bee-keeping and much helpful information can be obtained from large dealers in bees and bee supplies.

Observations.

1. How do bees protect their hives from rain and storm and light?
2. What are honey boxes? Where are they placed in the hive? Can the honey be removed late in the fall?
3. How is it safe to approach and handle bees in removing honey and caring for them?
4. What are their habits in entering and leaving the hive? What is the appearance of a returning loaded worker bee?
5. How do bees survive the winter? Why are the drones driven away or killed?
6. Watch bees gathering nectar and pollen from flowers and describe the process. Try following a bee on its journeys.
7. When the bees are in the hive, how may you know the queen and drones from the workers?
8. What is swarming? When does it take place? How is the swarm hived?
9. What is the home of wild honeybees? How found?

Summary of the Study of Honeybees

How is the work of the community of bees divided among the bees? How is each fitted for the work? What do you think of the success of this kind of life? Give reasons for your answer.

7. GENERAL STUDY OF INSECTS[1]

Materials.

Both living and preserved specimens of the insects studied should be at hand, if practicable. There also should be specimens of the young.

Observations.

The Body.

1. What is the shape and size of the insect and the number of regions in its body? Does the shape seem to be in any way adapted to the mode of life of the insect? If so, how?

Locomotion.

1. What methods of locomotion has the insect? Which is the most used?
2. What is the position of the wings when at rest? What is the texture (e.g. thick, smooth, leathery, shell-like, membranous) of the fore and hind wings?
3. For what kind of locomotion are the legs fitted? How?

Sense Organs.

1. How many antennæ has the insect? What is their character as to shape and length? How many simple and compound eyes?

Feeding.

1. What is the food of the insect? How are the mouth parts specially adapted to obtaining this food?

   Note.—The mouth parts of insects may be jaws for biting, or may form a tube for sucking, or a beak for piercing and sucking.

Respiration.

1. Look for movements of the body indicating breathing, and describe what you find. Discover the location of the spiracles.

Protection.

1. What are the enemies of this insect? (Among the most important enemies of insects are birds, certain other insects, and various small vertebrates such as frogs, snakes, lizards, turtles, etc.) How does the insect protect itself from these enemies?
2. Describe the shell with respect to thickness and flexibility. What is the character of the surface as to roughness or smoothness or covering of hairs or scales?

Reproduction and Development.

Note.—It may be necessary to get answers to these questions from books.

1. Where are the eggs deposited? What is the number of the eggs? How soon do they hatch?
2. What is the food of the larva or nymph? Are the food habits of the insects harmful to man? If so, how?
3. Describe the larva as to form, color, and appendages. Is it capable of locomotion?
4. Is the metamorphosis complete or incomplete? If complete, describe the pupa and tell where it may be found.

Drawings.

There should be one drawing of the insect to show its general characteristics; usually a dorsal view is best. For other drawings ask your instructor.

8. A REVIEW OF INSECTS

Summary of Important Points from the Table

1. What characters are common to all the insects described in the table?
2. What are the various types of wings? Why do they vary?
3. What are the various types of legs? How are they characterized?
4. What are the various types of mouth parts?
5. Show how the variations in insects are related to the habitat and mode of life of the insect.

9. KEY TO THE PRINCIPAL ORDERS OF INSECTS

Note 1.—When wings are folded, it will be helpful to remember that thickened fore or cover wings always have membranous wings folded beneath them.

10. SUMMARY OF THE STUDIES OF INSECTS

1. Take some insect for illustration, as the house fly, mosquito, tussock moth, or aphis, and show how insects increase in numbers with great rapidity.
2. What can be said about the number of species of insects?
3. There is said to be great competition among insects. Why? For what?
4. How is the great increase of insects held in check by natural means?
5. What are the various habitats of insects? Give as many as you can with examples of insects that use the habitat.
6. Give examples to show how greatly the food of insects and the method of obtaining it varies.
7. Give some illustrations of the great muscular development of insects. Why is this needed?
8. In what various ways are insects protected against their enemies? Give examples to illustrate your statement.
9. Show how and why the great numbers of insects have affected the structure and mode of life of the insects.

Classification

1. By means of illustrations from your studies of insects show how classification is based upon likeness of structure.
2. In the same manner show how differences in structure affect classification.
3. Show how variation in the wings and mouth parts is used to separate insects into orders.
4. What are the principles of classification?

11. REVIEW AND LIBRARY EXERCISE ON INSECTS

1. General characteristics of insects.
2. Principal orders of insects with characteristics and examples of each order.
3. Respiration and air sacs of insects. Use of air sacs in flight.
4. The heart and blood of insects. How the function of the blood differs from that of other animals, as man.
5. Special senses of insects: their character, location, and efficiency.
6. Sound-making organs of insects.
7. Power of communication among insects, as among ants, for example.
8. Organs for depositing eggs, ovipositors. How they vary.
9. Homes of insects. Evidences of architecture in some of the homes.
10. How some plants make homes for insects. Galls and gall insects.
11. In what various ways do insects survive the winter? Illustrate with examples.
12. Community life among insects. Types of communities.
13. Pollination of flowers by insects. Why insects do this work and how the flowers compel them to do it in the right manner. Value to the plants. Types of insects useful for this purpose.
14. Adaptations for protection against enemies. Classify these adaptations and illustrate with examples.
15. The principal insect pests of the orchard and their work.
16. The principal insect pests of the garden and the work of each.
17. The principal insect pests of shade trees and their characteristics.
18. The principal insect pests of the household and methods of extermination.
19. The work of birds in helping to keep the number of harmful insects down.
20. A spraying table showing what poisons are used, when and for what plants and insects.
21. The principal beneficial insects and the ways in which they are beneficial.

Special Topics

Much of the information called for by the topics below may be obtained from United States and state government bulletins. Most of these may be obtained free from the Department of Agriculture and from various state agricultural colleges, while others may be obtained by purchase at a nominal price.

Orthoptera.

1. Locust migrations and their cause.
2. The locust plagues of the "great plains."
3. Crickets and their "songs."

Hemiptera.

1. The fight against the orange scale of California.
2. History of the introduction and spread of the San José scale bug and the efforts to find a natural enemy. How people fight the pest.
3. Aphids.
4. Relations of ants and aphids.
5. Phylloxera and its work.
6. The methods of fighting the chinch bug.
7. Scale bugs.
8. Cochineal bug and the lacs.

Coleoptera.

1. The carrion beetle and its peculiar habits.
2. Fireflies.
3. Egyptian scarabs.
4. The curculio and methods of fighting it.
5. The weevils and their work.
6. History of the Colorado potato beetle.
7. Lady-bird beetles, their habits and use in exterminating harmful pests.

Diptera.

1. The investigations in Cuba of the cause of yellow fever.
2. The fight against yellow fever in New Orleans.
3. Methods of preventing plagues of mosquitoes.
4. How flies are carriers of disease. Methods of preventing plagues of flies.
5. The tsetse fly.
6. Sleeping sickness.
7. The house fly and typhoid.
8. Parasitic larvæ of flies.

Lepidoptera.

1. The silkworm and the silk industry.
2. Story of the gypsy moth.
3. Life history of the clothes moth.
4. Harmful butterflies.
5. The tussock moth and its history.
6. Blastophaga and fig culture.
7. The codling moth and its work.
8. Cutworms.
9. The brown-tail moth.

Hymenoptera.

1. The honeybee and honey making.
2. Gall and gall insects.
3. The habits of the digger wasp.
4. The homes of ants. Habits of ants.
5. Slavery among ants.
6. Agricultural ants.
7. Homes of bees.
8. Ichneumon flies and their beneficial habit.
9. Evidences of intelligence among ants.

SOME COMMON BUTTERFLIES—A Reference Table and Key

CHAPTER III
THE CONNECTION BETWEEN STRUCTURE AND FUNCTION

1. A STUDY OF THE CELL AND OF PROTOZOA

Cell,

the smallest living unit.

Protoplasm,

the living material composing the cell.

Nucleus,

a dense bit of protoplasm, usually near the center of the cell, often staining dark.

Cytoplasm,

the less dense protoplasm outside of the nucleus, usually taking a lighter stain.

Nucleolus, paranucleus or micronucleus,

a very small, dense, dark-staining body, either within the nucleus (nucleolus) or near it (paranucleus or micronucleus)

Cell wall,

the lifeless membrane surrounding many cells, secreted by the protoplasm.

Food balls,

bits of food inside the cells of many one-celled animals, usually showing through the walls.

Food vacuole,

a small drop of water containing digestive material and a food ball.

Contracting or pulsating vacuoles,

small, clear spots in the cell, filled with water. In the living cell these disappear at intervals and then appear again.

Oral groove,

a funnel-shaped groove in one side of some one-celled animals, conducting food to the mouth. In paramecium it often shows as an oblique line when the animal rolls.

Gullet,

the inner end of the oral groove.

Cilia,

numerous minute, vibrating, protoplasmic hairs on the surface of many cells.

Respiration,

the passage of oxygen into the tissues of a living organism and of carbon dioxide out of them. These gases can pass through any thin, moist, organic membrane. When such a membrane separates two fluids which differ in the amount of oxygen they contain, oxygen passes to the fluid containing the smaller amount.[2] The same is true of carbon dioxide. Respiration is believed to occur in all living organisms.

Digestion,

the process of making food materials soluble, so that they can pass through membranes and be used to build up protoplasm. A few forms of cells are able to take in solid food and digest it in their protoplasm, but most cells can admit only fluid food.

Fission,

a method of reproduction used in all cells, by which a cell divides itself into two, usually through the center. In some one-celled animals this may be preceded by conjugation, when two animals unite temporarily and exchange nuclear substance; or in some forms two cells may fuse and the resulting cell may divide. Budding is a form of fission in which a small projection is formed on the parent cell and then cut off, making a new individual.

Protozoa (first animals),

animals of one cell, existing alone or in loose colonies.

Observations.

1. Examine a single cell, stained to show structure. Identify the nucleus, cytoplasm, and, if present, the nucleolus or the micronucleus, and the cell wall. Draw to show the form of the cell and the details of its structure. Label all details.
2. Examine some stained paramecia. Select a typical one and identify in it nucleus, micronucleus, cytoplasm, and cell wall or cell membrane. You may also be able to see vacuoles, looking like holes in the stained protoplasm. Give reasons for considering this animal to be a single cell. Draw one, to show its cellular structure. Label all details.
3. Clean a slide and cover glass, place a drop of water containing living paramecia on the slide, cover it, and examine. What structures do you see which you saw in the stained paramecia? What structures do not show? Identify any new structures you may observe. Identify also the leading end and the side containing the oral groove.
4. Describe the shape of the animal.

   What is the actual length of the animal?

5. After watching the animal for some time, describe the path followed by a given specimen as it crosses the field of the microscope. What reason can you see, if any, why this paramecium is moving? What external factors, if any, seem to determine the path it follows?
6. How rapidly do paramecia really move? What structures do they use in locomotion?

   How do they manage to move in one direction, instead of alternately backward and forward? How do they manage to move in a straight line, though their bodies are not symmetrical?

7. What is the food of the paramecia? How do they find it? Find a specimen at rest and watch the oral groove. Suggest a method by which food may be collected into it. If possible, note the process of swallowing, and the resulting food ball.

   Note.—If powdered carmine be placed in the water with some paramecia, it can be seen in the food balls a half hour or so later.

8. Where are the food balls located? Watch them in an individual until you notice their motion. Where are the larger food balls? the smaller ones? Assuming them to have been of approximately equal sizes when they were taken in, how can you account for differences now?
9. Where are the contracting vacuoles? How many are there? How often does one contract?

   What is their function?

10. As you have been studying paramecia, to what external influences (as contact, heat, light, etc.) have you seen them respond? How do they show it when they do respond? Is such a response an advantage to them or not? What would be the result if they were not able to detect changes in their surroundings?
11. Where does respiration occur in paramecia? Where do they obtain their supply of oxygen?
12. Among the paramecia you are studying you usually find at least one in the process of fission. Watch it until the halves separate, if you can. Compare the halves. Do they rank as parent and offspring? If so, which is which? If not, which are they, parent or offspring?
13. If you happen to find a pair conjugating, notice the process, as far as you can, in the living animals.

Suggested drawings.

1. A drawing to show all the details seen in the living paramecium.
2. A diagram to show the path followed by a paramecium to get around some obstacle.
3. Drawings to show that paramecia are constant in shape and yet flexible.
4. A drawing to show at least one stage in fission. This may be from a permanent preparation.
5. A drawing to show paramecia conjugating. This also may be from a permanent preparation.
6. Instead of all these separate drawings they may be combined into one. Represent the field of the microscope, and in it draw all necessary figures, to show the facts called for in the first five drawings and any other facts you have observed about living protozoa. Make the whole drawing to scale.

Summary of Important Points in the Study of Paramecia

1. Look back over your study of paramecia and list the different kinds of work you saw paramecia doing; also the kinds of work you infer they can do. What organs have they to use? When there is no organ to do a given thing, e.g. to digest food, how is the work done?
2. What conditions are favorable to paramecia? Why are they so numerous under favorable conditions?
3. What would you call a successful animal? Are paramecia successful? Give reasons why they are or are not.

Comparative Study of Protozoa

To enlarge your idea of what a cell can do, spend as much more time on the one-celled animals as your course will permit. Any stagnant water may furnish several kinds. By means of reference books, identify as many as you can. In each case notice:—

1. Its size, shape and general appearance, comparing and contrasting it with paramecium.
2. Its usual surroundings, i.e. the conditions it has to meet.
3. The means it has of finding out facts about its surroundings.
4. The means it has of adjusting itself to its surroundings. For example, is it stationary? If so, what does it do when conditions change? Is it locomotory? If so, how effective is its locomotion?
5. What is its food? How does it find food?
6. Can it do as many kinds of work as paramecium can? Can it do any that paramecium cannot do? If so, what?

Review and Library Questions on Protozoa

1. What are the characteristics which distinguish protozoa from other animals?
2. What are the classes of protozoa? Characteristics of each class?
3. What is digestion? Where does it take place in the protozoa?
4. What results from the fact that the amœba has no cell wall? (Give at least two points.)
5. In what ways are paramecia more specialized than amœba are? How does their greater specialization show in their work?
6. What different methods of locomotion are shown among protozoa? By what means is locomotion accomplished in each case?
7. What is encysting? Name some protozoa which encyst. How long may an encysted animal live? When do they encyst? Why?
8. Give methods of reproduction among protozoa. Which method is fitted for rapid multiplication, for withstanding drouth; for renewing vitality?
9. Many scientists speak of protozoa as immortal. What argument is there to support such a statement?
10. Why are no protozoa large animals? Give at least two reasons.
11. Why are protozoa so numerous? Why more numerous in stagnant water?
12. Where are protozoa found?
13. Why are protozoa so widely distributed?
14. Write the probable history of a piece of chalk.
15. What connection is there between protozoa and some polishing powders?
16. Where in the human body are malarial protozoa found? How are they transferred from one human being to another? Why is there likely to be more malaria in newly settled regions than in older ones? If you were obliged to spend some time in a region where malaria existed, what precautions would you take?
17. Name other diseases caused by protozoa. How are they fought?
18. What beneficial effect have some protozoa upon the water of stagnant ponds and ditches? How may some forms injure water for household purposes?
19. Give at least three reasons for thinking that protozoa are the most ancient animals.
20. Why are protozoa of great importance to the world?

2. A STUDY OF SPONGES

Body wall,

the outer wall in bodies of the many-celled animals.

Central cavity,

the cavity surrounded by the body wall in the simpler many-celled animals, as in the sponges.

Canals,

channels through the body walls of sponges.

Inhalent pores,

the outer ends of the canals.

Ostia,

the inner ends of the canals.

Osculum,

the large opening of the central cavity, at the distal end of the sponge.

Spicules,

tiny needles of mineral substance found in the walls of many sponges.

Fibers,

flexible threads of horny material found in the walls of many sponges.

Endoderm cells,

cells lining the canals. They have cilia or flagella (projections larger than cilia).

Ectoderm cells,

cells covering the outside of sponges and some other animals. In sponges it is believed that endoderm and ectoderm cells are able to exchange positions and functions.

Mesoglea,

a jelly-like layer between the endoderm and ectoderm layers. In the sponges this contains many wandering cells, probably from the other layers.

Porifera (pore bearers),

animals with many more or less independent cells, supported by solid skeletal parts and penetrated by a system of canals which open on the surface as pores.

Directions.

Study a simple sponge to see the shape, size, and point of attachment. Identify the osculum. In a diagram of a long section of a simple sponge identify the central cavity, body walls, canals, inhalent pores, ostia, and osculum. In a simple sponge cut like the diagram identify the same structures. Do the same for the toilet sponge.

Study a diagram of a portion of the body wall, considerably enlarged. Identify the endoderm and ectoderm cells, the spicules or fibers, and, among the spicules or fibers, irregular amœboid cells, sometimes called mesoderm cells.

Examine a fragment or section of each kind of sponge under the microscope. Notice the arrangement, shape, and length of the spicules and of the fibers.

Test both kinds of sponges by dropping a bit of each into weak acid, and noting the results. Also burn a bit of each and notice the odor.

Questions.

1. What is the shape of a simple sponge? What enables a mass of cells to retain such a definite shape?
2. What seems to be the composition of the skeletons? Why is one type of skeleton rigid and the other elastic?
3. Since sponges are attached for most of their lives to stationary objects, suggest means for obtaining food and oxygen, and for getting rid of waste matter.
4. Although individual cells are sensitive, a sponge as a whole is not. What connection has this fact with the fact that sponges are stationary?
5. Compare simple and complex sponges.

Suggested drawings.

1. A view of a simple sponge. Label everything shown.
2. A diagram of a simple sponge split in halves. Show by arrows the path followed by the water as it passes through the sponge.
3. A few spicules.
4. A few fibers.

Summary of Important Points in the Study of Sponges

1. What are two functions of the spicules or fibers?
2. What are at least two of the functions of the endoderm cells?
3. What can you suggest as functions for the ectoderm cells?
4. In what cases do cells show "team work" in accomplishing an object?
5. What degree of specialization is indicated by the fact that the cells may exchange positions and functions?
6. What work can any single cell of a sponge do? Compare the work done by such a cell with that done by a paramecium.
7. What work can a whole sponge do? Compare that with the work done by a paramecium.

Review and Library Exercise on Sponges

1. What are the distinguishing characteristics of Porifera?
2. Sponges were once supposed to be plants. In what respect are they plant-like? What made students finally class them as animals?
3. How do sponges reproduce? How are they distributed to new locations?
4. Where, as to depth of water, do most sponges grow? Where, as to oceans? Where, as to latitude?
5. What are some of the difficulties which confront a stationary animal? How are they overcome?
6. To what class of sponges do the "toilet" sponges belong? Why?
7. What conditions are necessary for toilet sponges to thrive? Where are the best ones found? Where are they most numerous? How are they collected? How are they prepared for market?
8. What is man able to do toward raising good sponges for market?
9. Using reference books and museum specimens, describe some especially odd sponges.

3. A STUDY OF CŒLENTERATES

To show cells working together more definitely than in Sponges

A Study of Hydra

Definitions.

Proximal end,

the end by which an animal is attached to an object.

Distal end,

the end opposite the proximal end.

Tentacles,

slender projections around the distal end.

Mouth,

the opening through the distal end, into the central cavity.

Bud,

a small hydra or other cœlenterate growing out from the wall of the parent.

Mesoglea,

a thin, gluey partition, without wandering cells, between the ectoderm and the endoderm.

Nettle cells,

very small cells, chiefly in the tentacles, easily identified in permanent preparations as clear cells with small hairs projecting from them. See text-books for details of their structure.

Spermary,

the region or organ where the sperm cells are formed.

Ovary,

the region or organ where the egg cells are formed.

Cœlenterates (hollow bowels),

sac-shaped animals, the digestive tract having only one opening; the body wall is of two layers.

Directions.

Take a small aquarium to your table, set it down carefully and leave it undisturbed. Identify a hydra and watch it for some time.

Observations on the living animals.

1. Describe the size and shape of a hydra when expanded. Disturb it slightly by shaking the aquarium a little, and describe its shape when contracted. Notice also the flexibility of the body. What do you infer concerning the hydra's possession of a skeleton? What advantage can it be to have a body so flexible?
2. How many tentacles has the hydra that you are studying? What does the hydra do with these tentacles when it is expanded? What is the probable object of such actions?
3. How does a hydra respond to contact? What seems to be the object of such a response?
4. Notice the location of the hydras in the large, undisturbed aquaria. Where are they placed as regards the light side of the aquarium? Of what value is such a response to light in their case?
5. How can a hydra locate the small animals which are its food?

   How can it capture them?

6. What motions may a hydra perform, while remaining attached by its base? What are the results of these movements?
7. If you have happened to see a hydra move from one place to another, describe the process. If not, give the facts which lead you to believe that it is able to do so. Suggest all the methods you think it may be able to use. What is your opinion of the hydra's power of locomotion? Of what use is it in getting food; in escaping enemies; in following the fluctuations of the water supply? If you had to class the hydra as either one, would you call it a stationary or a locomotory animal?
8. Study budding hydras. Compare the bud with the parent hydra as to size, form and number and size of tentacles. Notice whether the bud moves independently or only with the parent. When does it separate from the parent?
9. In hydras collected late in the fall you may see another method of reproduction. If such material is at hand, notice small swellings near the proximal end and others near the tentacles. Eggs are produced in the lower one, the ovary, and sperm cells in the upper one, the spermary. Refer to your text-book for further details.

Details of structure.

1. Using an entire mounted specimen and a section of hydra, identify the body wall and the central cavity. What is the extent of the central cavity? (Examine both the body and the tentacles.) Where does it open to the outside? What do you think is its use?
2. In the body wall, identify the endodermal and ectodermal layers of cells, separated by the mesoglea, which is usually stained more deeply. Study these cell layers carefully. What work ought each to do? What can you discover in its structure which would fit each layer to do its work?
3. In the tentacles, identify the nettle cells. Where are they? How are they arranged? About how many of them would be discharged if a small animal were to bump into a tentacle?

Summary of Important Points in the Study of Hydra

1. Name the different kinds of cells in a hydra. Which kind differs most from such a cell as the starfish egg? What work does this specialized cell do?
2. How much of a hydra's body may be set in action by touching a tentacle? Contrast this with the sponge. What do you infer concerning the nervous power of these two animals?
3. Look back over your notes and list the different kinds of work a hydra can do.
4. Can it do any more kinds of work than a paramecium or a sponge can? If so, give further details.
5. Can it do any of its work in any better way? Would you expect it to be able to? Why, or why not?

Suggested drawings.

1. Hydra undisturbed, and hydra after being touched or shaken.
2. A hydra in successive poses to show its flexibility.
3. A hydra taking food.
4. Hydras to show reproduction in one or both ways.
5. A section of hydra, showing details.

Comparative Study of Cœlenterates

1. How large is an individual specimen in the form you are studying? If the form is colonial, how large is the colony or portion of a colony you are studying? Estimate the number of individuals in it. Is the colony free-swimming or attached? If attached, to what is it usually fastened?
2. Compare the individual you are studying with a hydra, as to size and shape of the body, the location of the mouth, and the size, number, and arrangement of the tentacles.
3. Is there a skeleton? If so, describe it. What appears to be its use? In corals, notice the radiating partitions.
4. Has the specimen any nettle cells? If so, where are they located?
5. Are all the polyps of the colony alike? If not, how many kinds are there? How do they differ?

   What is each kind best fitted to do? What is the probable result of this differentiation?

6. What kinds of reproduction, if any, does the specimen you are studying show?

   Find out from books what other forms of reproduction are sometimes used by this animal.

Suggested drawings.

1. At least one drawing of each cœlenterate you study.

Summary of the Comparative Study of Cœlenterates

1. How may polyps in colonial forms differ from polyps which live singly?
2. What variations in methods of reproduction are shown in this group?
3. Which of the polyps you have studied shows the greatest differentiation? In what ways?
4. What characteristic do you find common to all the cœlenterates you have studied?

Review and Library Exercise on Cœlenterates

1. What are the characteristics which distinguish cœlenterates?
2. Give the classes of cœlenterates, with the characteristics and an example of each.
3. What enables a hydra to stick to a support by its foot?
4. What are the processes in a hydra by which food is captured, swallowed, and digested?
5. What is the chief fact of interest about Hydra viridis?
6. Why do hydras reproduce all summer by budding and in the late fall by eggs?
7. What change would have developed a hydra and its offspring into a plant-like colony instead of into a group of individuals?
8. Why are ctenophores more easily seen in the night than other cœlenterates are?
9. What relations may exist between hydroids and hydro-medusæ?
10. What are the advantages of a sedentary life? Of a locomotory one?
11. What is meant by the expression "alternation of generations"? Which animals are likely to develop alternation of generations, sedentary ones or locomotory ones? Why?
12. Give at least two differences between hydro-medusæ and true jellyfishes.
13. In the association between a hydractinia colony and a hermit crab, what advantages are derived by the hydractinia? by the crab? Define symbiosis. Give another illustration of it.
14. How are new coral colonies started? How are large colonies formed?
15. What are the conditions of life under which corals can grow vigorously?
16. Where are corals most abundant?

    Note.—Show by coloring the regions on a blank map of the world.

17. How may corals form a reef? Why do they, as a rule, form a reef instead of adding directly to the mainland?
18. Give Darwin's theory regarding the way a coral atoll may have been formed.
19. Where are fossil corals found in abundance? What does their presence prove?
20. What is polymorphism? Give an illustration. What may be a disadvantage of polymorphism? What may be an advantage?
21. In what ways is this group of economic importance?

4. A STUDY OF WORMS

To show cells associated even more closely than in cœlenterates, forming tissues and systems of organs.

A Study of Earthworms

The Living Earthworm

Anterior end,

the head end, usually the leading end.

Posterior end,

the end opposite the anterior end.

Ventral surface,

the lower surface, usually the one which contains the mouth.

Dorsal surface,

the one opposite the ventral surface.

Somites,

the rings or segments of which some animal bodies are composed.

Bilateral symmetry,

the symmetry usually shown by animals which have differentiated dorsal and ventral surfaces, and right and left sides. Animals which do not have such differentiated surfaces are usually radially symmetrical, but sometimes asymmetrical (without symmetry).

Girdle,

the somewhat transparent band frequently found near the anterior end of an earthworm.

Anal opening,

the posterior opening of the food canal.

Setæ (singular form, seta),

small bristles or stiff hairs. In the earthworm these are set in the body wall at definite intervals, and aid in locomotion.

Cuticle,

in the earthworm a delicate, shining cover over the body.

Egg capsules,

small, light-colored, spindle-shaped sacks, about the size and somewhat the shape of a grain of wheat, containing the eggs or young of earthworms.

Directions.

Take a living earthworm to your table and keep it damp by placing it in a wet tray or upon moist paper. Identify the anterior and posterior ends, the dorsal and ventral surfaces, and the right and left sides. Identify also the somites and the girdle, the mouth with its projecting lip, and the anal opening.

Observations.

1. Watch a living worm for some time. Does it seem to have a definite object in its moving? If so, what is it? Upon what sense or senses does it seem to depend for guidance? Which end usually leads? Why?
2. Over what sort of surface does it move most easily? Why? Watch it closely for some time and discover how it is able to move from place to place. (Suggestion. What is the function of the setæ in this process? How can you explain the alternate contraction and expansion of parts?)
3. From time to time, for perhaps a week, examine the leaves which were scattered where the worms could reach them. Have the worms moved them about at all? If so, where are the leaves left? Have any been eaten, in part or entirely? If so, is there any evidence of selection, either as to the kind of leaf or the portion of leaf eaten? If earthworms select food, what senses would be useful for the purpose? Have you any evidence that earthworms possess such senses?
4. Looking through the dorsal wall, notice the meandering red line, seen more easily in some regions than in others. This is the dorsal blood vessel. How long is it? Where is it wider? Where narrower? Notice its pulsations. How many times per minute does it pulsate? In which direction is the blood forced? Is there a corresponding ventral blood vessel? Place a small worm between two pieces of glass, so that you may see through it more easily, and identify the blood vessels encircling the digestive canal, near the anterior end. These are the so-called "hearts" of the earthworm. If possible, decide in which direction the blood flows through them.
5. The food canal, or alimentary canal, lies underneath the dorsal blood vessel, and is usually easily seen, especially if it is full of food. Notice it when the worm is fully stretched and again when it is contracted. How long is the canal? Why does it wrinkle when the worm contracts? Where does it open to the outside? Why does it need to?
6. Where do you infer respiration must take place in this animal? Why do you think so? What fits this surface for such a purpose? Why does an earthworm seem so uncomfortable when it is too dry?
7. Where do earthworms live? What conditions are necessary in their habitat?
8. When do earthworms usually leave their burrows? Why at that particular time rather than at another? Why does "the early bird catch the worm"?
9. What enemies do earthworms have? How are they protected against these enemies?
10. If you have found egg capsules when collecting worms, describe them.

External Morphology of Earthworms