254 PHYSIOLOGY. 



these are spread myriads of blood-vessels, like a fine net- 

 work. I The air which is contained in the water, is drawn 

 in witti it by the mouth, and forced, by the muscles of the 

 throat, through the opening leading to the gills, the filaments 

 of which are expanded and separated by the same process, 

 so that they receive the full action of the fluid as it passes 

 by them. When a fish is taken out of water, the reason he 

 cannot breathe is, that these filaments collapse, and adhere 

 together in a mass, and the air cannot separate them. 



26. The seal, porpoise, dolphin and whale, belong to the 

 class mammalia, and therefore have to rise to the surface of 

 the water to get air to breathe. It is this necessity which 

 exposes the whale to the harpoon of the fisherman ; for 

 such are his strength and swiftness, that, could he live en- 

 tirely under water, he might defy the utmost ingenuity of 

 man to capture him. 



Fig. 9. 



The above cut shows the mode of respiration in fishes. The gills 

 are seen bent over in the form of a feather : d is the auricle of the 

 heart ; c, the ventricle ; /, the bronchial artery ; g, g, the gills. The 





