248 VERTEBRATE ANIMALS. 



two pairs of limbs, but these are in the form of awl-shaped organs, 

 each supported by a single, jointed cartilaginous rod. The pectoral 

 limbs have a membranous fringe inferiorly, and the ventrals are 

 placed very far back. There is also a median fin behind, forming 

 a continuous fringe round the compressed tail, and supported by 

 cartilaginous rays. 



The skull is composed of distinct bones, and there is a lower jaw ; 

 but the notochord is persistent, and there are no bodies of vertebriE 

 developed. The respiratory organs are twofold, consisting, firstly, 

 of free filamentous branchife or gills, ccantained in a branchial 

 chamber, which opens externally by a single vertical gill-slit ; and, 

 secondly of true lungs, in the form of a double cellular air-bladder 

 communicating with the gullet by means of an air-duct or windpipe. 

 Sometimes, if not ahvays, there are rudimentary external gills as 

 well, placed on the side of the neck. The heart consists of a ven- 

 tricle, and of tiro auricles, divided from one another by an incom- 

 plete partition. Lastly, the nasal sacs open behind into the throat, 

 and do not form closed chambers opening only by the nostrils, as 

 they do in all other fishes except the Myxinoids. The two best- 

 known species are the Lepidosiren paradoxa from the Amazon, and 

 the L. {Protopterus) annectens from the Gambia ; but the former is 





Fig. 179. — Ceratodus Forsterit one of the Australian Mud-fishes, reduced in size. 



very rare and little known. They both inhabit marshy tracts, and 

 lioth appear to be able in the dry season to bury themselves in the 

 nmd, and to form a kind of chamber, in which they remain dormant 

 till the rains of the wet season set them free. 



In the flesh \A'aters of Queensland, Australia, are found two other 

 remarkable Mud-fishes, belonging to the genus Ceratodus. The 

 singular Ci'nitodns Fumtrri (fig. 179), often called the " Barra- 

 nmnda," grows to the length of six feet, and has the body covered 

 with very large cycloid scales. The fins are not awl-like, but con- 

 sist of a fringe of fin-rays sui-rounding a central lobe. The Barra- 

 munda seems to feed upon leaves, which it masticates by means 

 of curious undulated b(jny plates or " molars," of which each jaw 

 carries two. It ajipeavs occasionally to come to land, at which 

 times it doubtless breathes by means of its lungs ; but it has well- 

 developed gills also, and is essentially an aquatic animal. 



