AMPHIBIOUS VERTEBRATES 455 



more extensive. There is abundant testimony showing that this 

 fish actually does breathe air. For example, Semon, who has 

 recently studied the habits of Ceratodus in its native rivers, writes 

 as follows on this point (in In the Australian Bit^sh): — "As afore- 

 said, Ceratodus is a representative of the almost exterminated 

 class of Dipnoi or lung-fish ; that is to say, fish possessing gills 

 by which they breathe like other fish, but also an air-bladder, 

 the construction and function of which very much resembles that 

 of a lung. What does Ceratodus use this lung for, since it does 

 not go on land, and therefore is not forced to adapt itself to extra- 

 aquatic conditions of breathing and living. . . .? That the fish 

 uses its lung for breathing I noticed hundreds of times. Near the 

 river area it haunts one occasionally hears a dull groaning sound. 

 This is produced by the fish, which comes up to the surface at 

 certain intervals to empty the breath from its air-bladder and 

 to take in fresh air. I readily proved Ceratodus to be the author 

 of this strange noise when later on I kept the fish alive in great 

 barrels and self-dug water-holes. I then saw them appear at the 

 surface every thirty or forty minutes and lift the tip of their snout 

 above the water, at the same time uttering the afore-mentioned 

 grunting noise. Still I was unable to make out whether it is 

 produced by the expiration of the foul air or the inspiration of the 

 fresh, and how or where it originates." The author then goes on 

 to explain how the possession of a lung is related to the actual 

 conditions of life: "At the same time, like any other fish, Cera- 

 todus makes use of its gills, and is by no means able to exist 

 on land. If taken out of the water and prevented from getting 

 back, its gills soon dry up and the animal dies. Nevertheless 

 its lungs are of great importance to the fish during the dry season, 

 for when the water evaporates over a wide area and the river gets 

 reduced to some few water-holes, the dimensions of which natur- 

 ally decrease from day to day, an immense accumulation of river 

 inmates takes place within these last havens of refuge. The 

 water thus rapidly becomes foul and putrid by rotting animal and 

 vegetable substance, and the fishes die in numbers. Mr. W. B. 

 Maltby of Gayndah told me that he had once emptied a big but 

 not very deep water-hole, which was approaching dryness. The 

 little water at its bottom was filled with dead mullets, perches, 

 and other fishes, and the whole was putrid with fish corpses. 

 Some Ceratodus, however, which were contained in this pool were 



