THE FRESH WATERS 177 



the toad buries itself among withered leaves, 

 or in some dry spot, while the frog returns to 

 the pond or ditch and hides itself in a hole, 

 perhaps in a drain-pipe, it may even be in the 

 damp mud. 



But the frog has long ago lost its gills, and 

 its lungs are closed in winter by the shutting 

 of the nostrils. How then does it breathe, for 

 breathe it must, even though the fires of life 

 are very low ? The skin is exceedingly thin 

 and delicate, and there is a network of very 

 fine blood-vessels all over it, and the exchange 

 of gases used carbonic acid gas for fresh 

 oxygen, which is the essential part of breathing 

 takes place directly from these blood-vessels 

 through the skin. 



WATER INSECTS 



One more group we must think of for a 

 little the aquatic insects. 



All fully developed insects breathe air 

 through little openings on the surface leading 

 into fine tubes, called tracheae, which carry the 

 air to all parts of the body. Even insects 

 which spend their whole lives on and in the 

 water breathe in this way. They may be able 



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