212 



RESPIRATION 



the oxygen pressure is very low. Nitrogen and COg, on the other 

 hand, will diffuse inwards if their partial pressure is less inside the 

 swim bladder than in the blood, and outwards in the converse 

 case. The pressure of nitrogen in the blood is doubtless about 79 



Figure 60. 

 Section through secreting gland of swim bladder of Sciaena aquila, showing 

 the epithelial body and underlying layer of capillary network (f) with gas bubbles 

 distending the gas ducts of the epithelial body (Jager). 



Figure 6i. 

 More highly magnified portion of epithelial body shown in 

 Figure 60. A distended gas duct, with surrounding secreting 

 cells (Jager). 



