PROTOPTERUS. 



575 



Ceratodus sometimes attains a length of 6 ft. The body is elongated 

 and compressed, and bears a continuous vertical fin. The paired fins 

 are trowel-like. There are five gill-clefts, four internal gills, and a 

 hyoid half-gill. There are no external gills. 



The swim-bladder or lung is single. It is supplied with blood from 

 the fourth branchial arches, as is the swim-bladder of Polypterus 

 and Amia. It arises ventrally, but lies 

 dorsally, and is divided into compart- 

 ments. 



The auricle of the heart has a 

 dorsal fibrous ridge hinting at a divi- 

 sion. A similar incomplete septum 

 occurs in the ventricle, and the sinus 

 venosus is divided into a left pulmonary 

 and a right systemic portion. The conus 

 arteriosus is peculiarly twisted, and 

 contains a short longitudinal spiral 

 valve and numerous large "pocket" 

 (or "Ganoid") valves. 



Protopterus. This mud-fish 

 lives in the Gambia, Quilimane, 

 and some other African rivers. 

 It is mainly but not exclusively 

 carnivorous, and attains a length 

 of 2 to 3 ft. or more. It has 

 extraordinary ' vitality, surviving 

 severe wounds, long fasting, and 

 desiccation. It appears to be 

 most active at night, and to prefer 

 shallow water, swimming rapidly 

 with powerful tail - strokes, or 

 "walking" slowly along the bottom 

 with its filamentous fins moving 

 alternately on each side, somewhat 



like the legs of a newt. At short FIG. 308. Skeleton of Cera- 

 intervals it comes to the surface todus fin. From Gegen 

 to take mouthfuls of air, which 

 passes out again through the 

 opercular aperture. 



As the dry season approaches, Protopterus burrows into the earth to 

 a depth of about 18 in., coils itself up, and secretes abundant mucus 

 from its skin glands. This secretion forms a cocoon or capsule, with 

 adherent earth externally, with moist slime internally, and with a lid, 

 on which there is always a small aperture. Thus encapsuled, the 



38 



todus 

 baur. 



., Central axis ; r. t radials ; 

 /*., basal piece. 



