RESPIRATION 45 



of water just as successfully as normal specimens. He suggested 

 that breathing was carried on through the skin, a statement which 

 is not nearly so improbable as it sounds. Since respiration is 

 nothing more than an exchange of gases by the blood, there is 

 no reason why these gases should not penetrate through thin 

 membranes like the skin, and reach the blood contained in 

 the fine vessels situated therein. The remarkable Httle Mud- 

 skipper [Periophthalmus) of tropical countries spends a great 

 part of its time walking or skipping about on the mud-flats of 

 mangrove swamps at low tide in search of food, and is also 

 fond of climbing on to the mangrove roots themselves or of 

 basking in the sun perched on a stone in a pool (Fig. 34f). 

 While out of the water the large gill-chambers are kept filled 

 with air, and the tail is, more often than not, left hanging down 

 in the water, serving as an additional organ of respiration. These 

 little fishes have become so accustomed to a life out of the water 

 that they are said to be unable to live in what should be their 

 native element for any length of time. 



Another remarkable method of breathing is adopted by some 

 of the Loaches {Cobitidae) and the Mailed Cat-fishes {Loricariidae) , 

 which use the intestine for this purpose at times. The Giant 

 Loach {Cobitis) of Europe, known in Germany as the "Wetter- 

 fisch" (weather fish) on account of its susceptibility to atmo- 

 spheric changes, has been specially studied, and the process of 

 breathing found to take place in the following manner. The 

 fish rises to the surface, and by thrusting its mouth above the 

 water, swallows a certain amount of air, which is passed down 

 into the intestine. There is a bulge in the intestine just behind 

 the stomach which serves as a reservoir; the fine blood-vessels 

 lining the walls of this chamber extract the oxygen from the 

 air, and the latter is finally voided by the vent. 



It is well known that when the air dissolved in the water 

 fails a fish is obliged to ascend to the surface to avoid suffocation. 

 The habit of seeking oxygen by swallowing bubbles of air is 

 found in many different kinds of Bony Fishes, but in certain 

 forms living in shallow ponds and streams which dry up 

 periodically, or in pools rendered foul by decaying vegetation, 

 this gulping of air becomes a necessity if the fishes are to survive 

 at all. As a result, it is found that the intensification of the air- 

 breathing habit over a very long period of time has led to the 

 development of special accessory breathing organs in addition 

 to the gills, thus enabling the fishes to survive for a compara- 

 tively long time out of water. These organs take the form of 



