THE FROG. 



The following directions refer more particularly to Rana 

 pipiens, but can be used with other species of frog if desired. 



I. ATTITUDES AND MOVEMENTS. 



Notice the normal resting position of the living frog, 

 especially the attitudes of the fore and hind limbs. Induce 

 a frog to leap; how is this movement effected? Are any 

 preparatory movements required? What is the significance 

 of the normal resting position? Compare the frog's mode 

 of progression with that of a tailed amphibian (e. g., Ambly- 

 stoma). 



Describe the attitude of a frog resting at the surface of 

 deep water. How much of the frog is above water? What 

 is the advantage of the protrusion or bulging of the eyes? 

 Can the frog in this position secure air? When a frog in 

 this position is alarmed, it will dive quickly to the bottom. 

 Describe in detail the successive movements by which this is 

 accomplished. What is the significance of the resting posi- 

 tion at the surface of deep water? 



Study the respiratory movements and explain fully how 

 air is taken into and expelled from (a) the mouth, and (&) 

 the lungs. The frog does not possess ribs and is unable to 

 enlarge the cavity of the body directly; hence it employs an 

 indirect method of filling the lungs, which can be made out 

 by a careful study of the movements of (a) the floor of the 

 mouth, (&) the nares (nasal openings), and (c) the body. 

 The glottis, through which air passes from the throat into 

 the lungs, may be opened or closed as occasion requires. 



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