The Inhabitants of the Aquarium 139 



depend upon the gills for the taking in of 

 oxygen. The atmospheric air is taken in 

 through the mouth, forced down into the in- 

 testinal canal, where the oxygen is extracted, 

 the carbonic gas leaving the body through 

 the anal opening in the form of large bub- 

 bles which mount to the surface of the 

 water. 



The Cobitis, when supplied with a suffi- 

 cient amount of food, grows rapidly, even 

 outgrowing the aquarium, where it is desira- 

 ble only so long as it is of small size. 



Preceding any sudden change in the 

 weather, this fish exhibits great restlessness 

 and activity, a fact especially noticeable, as 

 it is usually sluggish and, if undisturbed, 

 often rests motionless for hours. It is from 

 this barometer-like disposition that it gets its 

 name. 



The Barbed Grundel (Cobitis barbatula) is 

 somewhat more delicate than the other 

 Cobitis. To keep it successfully the aqua- 

 rium must be well stocked with oxygenating 



