644 PHYLUM CHORDATA I CLASS PISCES — FISHES 



3 mm. in diameter and coated with jelly, are laid singly 

 amongst water plants. 



(2) Protopterus.^Protopterus is a less bulky fish than 

 Ceratodus, and commonly from 2 to 3 ft. long (Fig. 368). 

 The scales are smaller. The paired fins are slender and 

 tapering. There are five gill-clefts covered by an operculum. 

 Vestiges of the external gills of the larval stage sometimes 

 remain on into adult life. Protopterus is a voracious feeder, 

 mainly but not exclusively carnivorous, and from time to 

 time rising to the surface of the marsh to take mouthfuls 

 of air. It has extraordinary vitality, surviving severe 

 wounds, long fasting, and desiccation. It is most active 

 at night, swimming rapidly with powerful tail strokes or 

 " walking " slowly along the bottom with its slender fins 

 moving alternately on each side, somewhat like the legs 

 of a newt. As the dry season approaches and the marshes 

 become dried up, Protopterus burrows into the earth to 

 a depth of about 18 in., coils itself up, and secretes abun- 

 dant 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 animal 

 remains dormant for months. The air seems to pass 

 directly from the mouth of the burrow, through the aper- 

 ture of the capsule lid (which is produced inwards in a 

 short pipe) to the animal's mouth, and thence to the lungs. 

 During all this time Protopterus is living on its own tissues, 

 especially on fat stored round the kidneys and reproductive 

 organs and among the muscles of the tail {cf. fatty bodies 

 in caterpillars, amphibians, etc.). These capsules with 

 the surrounding earth have often been transported from 

 Africa to Northern Europe without injury to the dormant 

 fish within. When the rainy season begins, early in June, 

 the Protopterus emerges from its capsule. The eggs 

 — about 4 mm. in diameter — are deposited in a " nest " — 

 a water-filled hole about a foot deep on the margin of a pool. 

 The male guards the nest, aerating the eggs by lashing the 

 water with his tail. The larvae begin to hatch in about 

 eight days, but remain in the nest for another fortnight, 

 clinging by their cement-organs to the sides of the nest. 

 (3) Lepidosiren is the most eel-like of the Dipnoi 



