CHAPTER YI 



respiration, lungs, skin-breathing, circulation, 

 hearts, and lymph-hearts in amphibians 



Respiration 



Since amphibians liave no ribs to expand their 

 lungs, those which breathe air get their breath by 

 literally swallowing it, but they have muscles which 

 expel it. In the water-haunters with gills, the lungs 

 are mere sacs, without cells or pouches. In the cae- 

 cilians the left lung is small and nearly useless. All 

 the kinds which stay under the water long have cer- 

 tain places in the body where well aerated blood is 

 stored ; and a large blood supply runs to the skin 

 also. The skin aids the amphibians in breathing, 

 even where there are good lungs, as in the frogs. 

 To be thus useful it must be moist, like the gills of a 

 fish, so that frogs and toads especially have water 

 condensed into the body which they can cause to flow 

 out over the skin. 



In the tailed forms, the body has a " lateral line " 

 or series of pores along the side of the body, like that 

 of fishes, whence a secretion keeps the skin moist and 

 slick. They have many other mucus glands besides. 



We can thus see that frogs may breathe better 



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