124 THE BOOK OF NATURE STUDY 



squat, with a slight hump on the back (where the hip girdle articul- 

 ates with the last free vertebra), with the hind-leg bent like a 

 letter Z, the knee pointing forwards, the ankle backwards, the 

 tips of the toes forwards, and so on. 



It is very instructive to watch the respiration. When a frog 

 is breathing the nostrils are alternately opened and closed, the 

 under side of the throat is rhythmically lowered and raised, the 

 mouth remaining tightly shut meanwhile, and the flanks of the 

 body rise and sink. 



The pupils should watch the different movements and time 

 them, and draw inferences, (a) When the floor of the mouth 

 is lowered, and the buccal cavity thus increased, air passes in 

 by the open nostrils. There is a sort of suction-pump action. 

 (&) When the nostrils and the opening of the gullet are closed, 

 and the floor of the mouth is raised, the air is forced through 

 the open glottis into the lungs. There is a sort of force- 

 pump action, (c) When the pressure on the lungs is re- 

 laxed, and when the muscles of the sides of the body contract, 

 air passes from the lungs to the mouth and out by the open 

 nostrils. 



" To tell the pupils that such and such is the case, and 

 then request them to verify the statement is destructive 

 alike of interest and of the beneficial results which are the 

 aim of all science teaching. But it is quite legitimate, after 

 all that is possible has been found out, to impart a little 

 additional information by way of explanation of facts observed. 

 For example, supposing that the respiratory ^movements of 

 a frog be under notice, we may ask the class to describe 

 the movements of the throat, nostrils, ear-drum, and flanks, 

 to note the condition of the mouth, to time the frequency 

 of the various movements, and describe their relation one to 

 another ; but we shall not be wrong subsequently, by the 

 aid of a model and by blackboard diagrams, to get the class to 

 reason out, with a little assistance, how the air is forced into 

 the lungs by the compression exerted by the floor of the mouth 

 cavity. " l 



1 O. H. Latter, see references, p. 135. 



