Questions.
  1. Name the parts of the frog's alimentary canal.
  2. Name the glands or organs which are accessory to the canal.
  3. How long is the esophagus? How does the presence or absence of a neck affect the esophagus?
  4. How does the thickness of the stomach wall compare with that of the intestine, and how do you account for the difference?
  5. Measure the length of the trunk of the frog's body and that of the outstretched alimentary canal. How many times the length of the one is that of the other? How does this ratio compare with that of an herbivorous animal? (The sheep's food canal is about thirty-two times the length of its body.)
  6. What is the color of the bile, as seen through the walls of the bile sac? This color is characteristic of carnivorous animals; in herbivorous forms it is yellow. Find its color in some omnivorous form, as man.
  7. Name the organs concerned in excretion.
  8. What holds the internal organs in place, and from what are they suspended?
  9. The spleen is called a "ductless gland." Give its function, and explain why a duct is not necessary to it.
  10. Since the frog swallows its food alive and entire, what work must the stomach do? What digestive organs would be absent from the mouth, or else poorly developed?
  11. Since the frog is carnivorous, what digestive ferments are probably present, and what ones absent from the alimentary canal?
  12. Fat bodies are largest in the fall, and are rarely found in the spring. How can you account for this?
  13. When through with the general study of the alimentary canal, you may open the stomach by cutting it lengthwise. Describe the character of the stomach lining as to folds and villi, stating the advantage of each being present and the reason for the direction of the folds. Tell how the food is propelled onward through the alimentary canal. Give the scientific name for this action.
Suggested drawings.
  1. The viscera (internal organs) undisturbed.
  2. The alimentary canal extended.
  3. The excretory system.
The Organs of Circulation and Respiration of the Frog
Materials.

The materials used in this exercise are the same as those used in the preceding exercise.

Observations.

The pupil should identify the following structures:—

Pericardium, a membrane that surrounds the heart and, in the case of the frog, separates the body cavity into two portions, the abdomen and the pericardial chamber. Heart, lying between the shoulders and in front of the false diaphragm. It is conical in form and composed of three chambers. Ventricle, the pink, conical, and muscular portion of the heart, pointing backward and outward. Auricles, right and left. These are anterior and dorsal to the ventricle, thin, membranous, and dark-colored. Arterial trunk, the single large blood vessel, usually empty of blood, and white. Note its origin and trace it as far as possible, at least until you see it divide to encircle the throat. Sinus venosus, a large membranous sac dorsal to the heart and connected with the right auricle. Lungs, two small oblong, pink, spongy sacs, lying between and behind the shoulders.