2. Show how variation in habitat depends upon structure among rodents by comparing, for example, squirrels, beavers, and woodchucks. 3. Variations in the tails of rodents. What are the causes of this variation? 4. Pocket gophers and their economic relations. 5. Species of mice. Their habits. 6. The dancing mouse. 7. Damage by mice. Plagues of field mice in Nevada. Method of extermination. 8. Habits and kinds of rats. 9. Economic importance of rats. Methods of extermination. 10. Rats and the bubonic plague. 11. Squirrels, kinds and habits. 12. The economic value of rabbits. 13. The groundhog myth. Habits of woodchucks. 14. The beaver--their habits and sagacity. Methods of trapping them. 15. Prairie dogs--their habits and economic importance. How exterminated? 16. What are porcupines? 17. Variation in the homes among rodents. Usual means of defense. 18. Make a list of rodents in a column, and in another column opposite each name write the various ways the animal is of economic importance. Sum up with a statement showing the most important ways rodents are of value to man and harmful to man. 19. Defend the proposition that rodents are on the whole harmful animals and should be exterminated. 20. How some rodents contribute to the science of medicine, more especially to bacteriology. The Cat or Dog--Carnivora _Materials._ Living specimens of cats or dogs. Pictures, books, lantern slides, etc. Supplement the laboratory study with trips to museums and zoölogical gardens to observe the relatives of the cat. _Definitions._ _Carnivora._ An order of mammals, chiefly flesh-eating, with claws and well-developed canine teeth. _Carnivorous_, flesh-eating. _Herbivorous_, plant-eating. _Omnivorous_, eating both plants and animal food. _Digitigrade_, walking on the toes. _Plantigrade_, walking on the soles of the feet. _Vibrissæ_, long hairs on the face--"whiskers." _Observations._ 1. Into what regions is the body divided? 2. What is the shape of the head and the length of the neck? 3. Are the legs relatively long or short? How do the front and hind legs compare in length? How many toes on each foot? Is the cat digitigrade or plantigrade? 4. How many pads on the sole of the foot? What use can you suggest for these structures? What is the size and shape of the claws? Are they retractile or nonretractile? For what purposes may the claws be used? 5. Describe the tail as to length and appearance. Movements. 6. What is the size and appearance of the external ears? What movement do you notice? 7. Are the eyes large or small? What eyelids can you find? What other accessory structures? What is the shape and direction of the pupil? 8. What other sensory structures do you find? What is their function? 9. Watch the animal eat. Does it chew or "fletcherize" its food? What teeth seem well developed? Is the movement of the jaws simply up and down, or is there a lateral movement as well?