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 issingle. It is supplied with blood from 
the fourth branchial arches, as is the swim-bladder of Polypterus 
and Ama. 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 Fic. 308.—Skeleton of Cera- 
intervals it comes to the surface “sen fin.—From Gegen- 
to take mouthfuls of air, which 0 asics» eadiale: 
passes out again through the 7", ‘fasal pies, 
opercular aperture. 
As the dry season approaches, Protogerus 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 
