512 FISHES. 



It must be noted, however, that it does not follow that 

 the Dipnoi are the connecting links between Fishes and 

 Amphibians because they possess certain characters of 

 both these classes. We require further palseontological and 

 embryological evidence. The Dipnoi are physiologically 

 transitional between Fishes and Amphibians, having, for 

 instance, acquired lungs while retaining gills, but it does 

 not follow that they are morphologically transitional. 



(a) Ceratodus. 



The genus Ceratodus is abundantly represented by fossils 

 in the Mesozoic beds of Europe, America, Asia, and 

 Australia, but the living animal is now limited to the basins 

 of two of the rivers of Queensland. C. forsteri, the best 

 known and perhaps the only species, was first described by 

 Krefft in 1870, and recently (1891) its habits have been 

 studied by Professor Richard Semon of Jena. Like that 

 other old-fashioned animal the duckmole, Ceratodus fre- 

 quents the still deep places of the river's bed, the so-called 

 "water-holes." At the bottom of these it lies sluggishly, 

 occasionally rising to the surface to gulp in air. Its diet 

 was formerly supposed to be exclusively vegetarian, but 

 Semon holds that it crops the luxuriant vegetation of the 

 river-banks only for the sake of the animal life larvae and 

 eggs of insects, worms, molluscs, amphibians, and fishes 

 contained among it. Certain it is, that natives and colonists 

 catch it by means of animal bait. From this method of 

 angling for it, and from its rosy-tinted flesh, considerable 

 confusion has arisen between Ceratodus and a Teleostean 

 fish, the true Barramunda or Dawson salmon, found in 

 some of the Queensland rivers. Ceratodus is quite unable 

 to live out of water, but its air-breathing powers enable it to 

 exist in water which is laden with sand or rotten vegetable 

 matter. According to Semon, its limited distribution is to 

 be accounted for, first, by its sluggish nature, for it comes 

 of a dying stock ; and, secondly, by the fact that the eggs 

 are very readily destroyed, and so incapable of distribution 

 by any of the ordinary means. Nothing is known of the 

 process of fertilisation, but the eggs, which are surrounded 

 by a jelly-like envelope, are laid singly in the water. The 

 development has not yet been fully worked out, but seg 



