nesting places of bluebirds, wrens, tree swallows, and martins. (Fig. 77.)

1 For other methods of encouraging birds see Weed and Dearborn, "Birds in their Relations to Man," pp. 304-315. Trafton, "Methods of Attracting Birds," and leaflets of National Associa tion of Audubon Societies, 1974 Broadway, N. Y., e.g. No. 16 (Winter Feeding of Wild Birds) and No. 18 (Putting up Bird Boxes), 1 cent each.

CHAPTER III

FROGS AND THEIR RELATIVES

81. Study of the frog. Laboratory study.

A. Regions and appendages. The frog's body consists of two principal parts, or regions; namely, the head and trunk. The line of union between the two regions is just in front of the anterior appendages (arms).

1. Locate the appendages (arms and legs) attached to the trunk.

2. Name and locate the organs that you find on the head, giving the number of each.

B. Breathing organs.

1. Describe the location of the nostrils on the head.
2. Examine a preserved specimen in which a stiff bristle
has been passed through one of the nostrils.

a. Tell what was done.

b. Into what cavity has the bristle emerged?

c. (Optional.) What is one difference, therefore, between the nostrils of a fish and of a frog? (See 102, 2 b.)

d. In what region (anterior or posterior) of the roof of the mouth cavity are the inner openings of the nostrils located?

3. (Demonstration.) Just back of the tongue there is a narrow opening that leads into the windpipe (trachea). This opening is called the glottis.

a. Locate the glottis.

b. Does the glottis extend lengthwise or crosswise of the mouth cavity?

c. Into what does the glottis open?

4. Examine a dissected frog prepared in such a way as to show the lungs.

a. State the location of the lungs with reference to the head and the cavity of the trunk.

b. Describe the appearance of the lungs.

c. Insert the end of a glass tube, that has been drawn out to a small diameter, into the glottis

opening and blow air into the lungs. Describe what you have done and state the result.

5. Name in order the openings, the cavity, and the tube through which the air must pass in order to reach the lungs.

C. Breathing movements.

1. Place a frog in a glass jar with an inch or two of water and watch the action of the floor of the mouth.

This is one of the breathing movements. Describe this breathing movement of the frog. 2. There are two breathing movements of the sides of the trunk, one a very active inward and outward movement, and the other a very slight inward and outward movement. When you have seen these two kinds of movements of the sides, describe them and state which kind occurs the more frequently.

D. How the frog exhales.

1. What effect will the active inward movement of the sides have upon

a. The size of the body cavity?

b. The size of the lungs?

c. The pressure of the air in the lungs ?

2. When the sides of the trunk move actively inward, will the air move into the lungs or out? Why?

3. Through what passages will the air go from the lungs to the outside of the frog?

a. Will the size of the mouth cavity be made larger

or smaller?

b. If the nostrils are now open will the air move into the mouth cavity or out? Why?

2. When the floor of the mouth is raised

a. Will the size of the mouth cavity be increased or decreased?

b. Will the pressure of the air in the mouth cavity be increased or decreased?

c. If both the nostrils and the glottis are now open, in what directions will air be forced?

d. What causes the slight outward movements of the sides of the trunk in the region of the lungs?

F. How the lungs are fitted for breathing organs. (Suggested as home work.)

When the lungs are inflated (see B, 4 above) they look like bags (Fig. 80). The lungs are hollow, and their walls are composed of thin material. In these membranous walls are thinwalled blood vessels known as capillaries. The heart forces blood that has come from the body into these capillaries of the lungs, and then back to the heart. Bearing in mind that respiration in animals is essentially the same as in plants (P. B., 82)

1. State what waste substance the blood brings to the lungs to be given off from the capillaries.

2. What gas will the blood in the capillaries take up from the air in the lungs?

3. How are the walls of the lungs and of the capillaries of the lungs fitted by structure to make this interchange of gases possible?

G. Food-getting.

To the Teacher. -Select a number of as large preserved or freshly killed frogs as you can get. Open the jaws as far as possible and keep them in this position by means of small pieces of wood.

1. Seize the posterior or hind end of the tongue and pull it forward.

a. Tell what you have done and state which end of the tongue is attached to the floor of the mouth. b. Describe the shape of the tip end of the tongue. 2. The living frog can extend its tongue much farther than you have been able to do in the case of the preserved frog, and in the living frog the tongue is covered with a very sticky substance. The tongue is used to catch insects at some distance from the animal (Fig. 79). Tell how you think the frog could use its tongue to catch insects and get them into its mouth.1

3. Look for teeth on the jaws of a skeleton of a frog, or if you cannot obtain a skeleton, rub the finger over the jaws of a preserved specimen.

a. Which of the jaws has teeth?

b. Describe the location of the teeth on the jaw.
c. State the shape and size of the jaw teeth.

d. What is the probable use of the jaw teeth?

4. (Optional.) Look on the roof of the mouth for two relatively large palate teeth. Rub the fingers over the surface of the palate teeth.

a. Tell what you have done.

b. What have you found out about the palate teeth?
c. What is the probable use of the palate teeth?

H. How a frog swallows.

1. Gently touch the eyes of a living frog until it draws them into the head. Tell what you have done and observed.

2. Look at the roof of the mouth of a preserved specimen while you push the eyes into the head. Tell what you have done and describe the effect produced in the roof of the mouth.

3. How will the act of pushing the eyes into the head be useful to a frog in swallowing?1

1 If possible live frogs should be fed on meal worms, or other insects, and the feeding movements observed.