44 



5* ithout difficulty, rise of* sink in the water. In 

 fresh water fish, this bladder contains, according 1 

 to ERMAN T S experiment, nitrogene gas, mixed 

 with varying portions of oxygene gas, which is, 

 however, never found in it in the same propor- 

 tion as in atmospheric air. BIOT found, on the 

 contrary, that in salt-water fish it contained oxy- 

 gene gas, increasing in proportion as the fish was 

 in the habit of living at a greater depth, so that 

 in fishes, which were caught in water 1000 me] 

 tres deep, the air contained from 1 to TO of oxy- 

 gene gas. In the bladder of such fish, the air is 

 so compressed by the heavy column of water 

 above, that when the fish is drawn up, the bladder 

 swells and forces the stomach through the mouth. 



o 



In one kind of fish, the colitis fossilis, EKMAN 

 observed a doub ] respiration. Ii: water, con- 

 taining air, the fisti breathed as usual, through 

 its gills -, but if the water was deprived of its por- 

 tion of oxygene gas, the fish rose above the smv 

 face, drew air through its mouth and swallowed 

 it. This air penetrated tjie intestines, the blood 

 vessels of which were reddened, and when it had 

 lost its portion of oxygene gas, the fish discharged 

 }t by the rectum. 



The respiration of insects was very carefully 



