LUNG FiaHES. 



429 



Pig. 393.— External gills of a young Po- 

 lypterus bichir. &r, extL-rual gills. 



many-jointed cartilaginous rod, to which is attached fine fin- 

 rays, supporting the thin edge of the fin. 



The spiral valve is present in the intestinal tract, ending 

 rather far from the cloaca, into which the oviducts and ure- 

 ters both open. There is a muscular conus arteriosus, and 

 the heart has besides the right large auricle, a left smaller one 

 which receives the blood from the lungs, and a single ven- 

 tricle, as in Amphibians and most reptiles ; they have true 

 nostrils. The lungs are like those of Amphibians, and in 

 addition they possess both 

 internal and external gills, ^\ 



the latter nearly or wholly 

 aborted in the adult. 



The genus Ceratodus was 

 originally named by Agassiz, 

 from teeth found in Jurassic 

 and Triassic strata in Eui'ope. Living specimens were found 

 by Mr. Krefft in Queensland, Australia, and called Geratodus 

 Fosteri KrefEt (Eg. 394). This fish is rather more elemen- 

 tary in form than Lepidosiren, the body being stouter, and 

 the large scales of the body, with the fin-like paddles and 

 distinctly rayed vertical fins, cause it to resemble more closely 

 ordinary bony fishes than Lepidosiren (Gtlnther). Moreover 



Fi I I I ;.) 



the lung is single, and not used so much as the two perfect 

 lungs of Lepidosireyi. It attains a length of six feet. It 

 can breathe by either gills or lungs alone. When, Gtlnther 

 thinks, the fish is compelled to live during droughts in thick 

 muddy water charged with gases wliicli are the product of 

 decomposing organic matter, it is obliged to use its lungs. 

 The gills are more like those of ordinary bony fishes than 

 those of Lepidosiren. It lives on the dead leaves of aquatic 

 grasses, etc. The local English name is "flat-head," tho 



