OF RESPIRATION. 1 25 



ihe hard shell, whilst in polyps they peiforate the A'alls of 

 the ge.ieral cavity of the body, which they constantly fill 

 with v\ater. 



of Vertebrates. In those Radiates which are provided with distinct 

 respiratory organs, such as the Echinoderms, we find still another 

 typical structure, their gills forming bunches of fringes around the 

 mouth, or rows of minute vesicles along the radiating segments of 

 Ihe body. 



11* 



