320 ZOOLOGY 



the parts of the body in swimming and in its other methods of 

 locomotion. Can it rest at the surface of the water? How 

 much of the body protrudes from the water? How does it 

 dive? Can you find any evidence that it does anything to 

 increase its specific gravity when diving? 



Feed by placing living grasshoppers or flies in the vessel 

 with a frog, or by dangling a piece of meat in front of it at 

 the end of a string. Note the action of the tongue in making 

 the capture. Examine the mode of attachment of tongue, 

 and suggest its possible advantages. 



Watch the animal while floating at the surface of water or 

 out of water. Can you detect any signs of breathing? Note 

 carefully the nostrils, the cheeks and the sides of the abdomen, 

 and determine how it gets air into its lungs. Prove your con- 

 clusions. Determine what senses are represented in the frog. 

 How does it react to salines, acids, sweets, bitters? Judging 

 from the position of the eyes and from experiment, can a frog 

 on the ground see objects in all directions ? Can it do so while 

 floating on the surface of the water? Are the eyes movable? 

 Can the frog see any point with both eyes at the same time? 

 What happens if a frog is placed on his back ? Explain. Does 

 the frog seem to have any sense of elevation when he comes to 

 the edge of a table? How do you estimate this? By experi- 

 ment and by reference determine whether the frog's actions are 

 at all modified by experience. 



Select a small frog and chloroform it until quiet, but not 

 enough to kUl it. Wrap it in a wet cloth, and place on a support 

 of such height as will allow the web to be stretched over the open- 

 ing in the stage of the microscope. With the lower power note 

 the pigment cells and blood vessels. Determine which are 

 arteries and which veins; present your evidences. By placing a 

 little water and a cover-glass on the web the high power may be 

 used, and the behavior of the corpuscles studied as they pass 

 through the capillaries. Similar studies may be made on the 

 gills of very young tadpoles. 



B. External Anatomy. — What is its symmetry? Compare 

 carefully the structure and form of the dorsal with that of 

 ventral surface; similarly those of the anterior and posterior 



