140 VITAL FUNCTIONS. 



lion is performed by the skin But in those which are A 

 step above these, we find some special preparations for 

 this function. In the Mollusca the organs of respiration 

 are situated near the outer margin of the shell, and con- 

 sist of parallel filaments arranged like the teeth of a fine 

 comb. These are called branchia or gills. 



417. Respiration of the Oyster. These organs are 

 represented by Fig. 88. Their mechanism, when closely 

 Fig. 88. 





examined, is exceedingly curious, and somewhat intricate. 

 There is a triangular canal, d, which leads through the 

 whole length of the organ w 7 here it is attached to the 

 body. By means of this, the water is admitted to the in- 

 terior of the gills generally. Beside this provision for the 

 admission of water, by a sort of canal, there are numerous 

 small apertures, e, by which the fluid is sent to every 

 feather of the gills. The parts ff, are the feathery ex- 

 tremities of this organ, which appear like a treble fold of 

 some fine fabric, suspended like a festoon. 



4 18. After the water thus admitted into the branchia has 

 performed its office of aeration, it is again expelled by a 

 different opening. 



419. Another step in the scale of animal existence, 

 brings us to the Fishes, the branchial apparatus of which 

 is much more complicated and important than that of the 

 Mollusca. In these, the respiratory action is more essen- 



What are the respiratory organs called in the mollusca and fishes ? 

 How is respiration performed in the oyster ? 



