20 SCIENCE PRIMERS. [§ ik 



into the stomach. Then it narrows again into the 

 intestine, and after winding about inside the cavity of 

 the abdomen a good deal, finally leaves it. 



You see the alimentary canal (for that is the name 

 given to this long tube made up of gullet, stomach, 

 intestine, &c.) o;oes right through the cavity of 

 the body without opening into it — very much 

 as the tall narrow glass of a lamp passes through the 

 large globe glass. You might pour anything down the 

 narrow glass without its going into the globe glass, 

 and you might fill the globe glass and yet leave the 

 narrow glass quite empty. If you imagine both 

 glasses soft and flexible instead of hard and stiff, zx^^ 

 suppose the narrow glass to be very long and twist ' 

 about so as to all but fill the globe, you will have a 

 very fair idea of how the alimentary canal is placed in 

 the cavity of the body. 



Besides the alimentary canal, there is in the chest, 

 in addition to the windpipe and lungs, the heart with 

 its great tubes, and in the abdomen there are the 

 liver, the kidneys, and other organs. 



These two great cavities, with all that is inside the n, 

 together with wrappings of flesh and skin which make 

 up the walls of the cavities, form the trunk, and on 

 to the trunk are fastened the jointed legs and arms. 

 These have no large cavities, and the alimentary canal 

 goes nowhere near them. 



One more thing you have to note. There is only 

 one alimentary canal, one liver, one heart — but there 

 are two kidneys and two lungs, the one on one side, the 

 other on the other, and the one very much like the other. 

 There are two arms and two legs, the one almost 

 exactly like the other. There is only one head, but 



