ORIGIN OF THE LAND VERTEBRATES M 



other animals in the swamp, but as the drought 

 approaches feeding ceases, the animal burrows into 

 the wet mud and fashions a kind of cocoon for itself 

 with a small opening to the air protected by a lid. 

 Curled up in this cocoon with its tail folded over its 



,f 



Fig. 21. Ceratodus forsteri. f. median fin ; pf. pectoral fin ; pv. pelvic 

 fin; bo. branchial opening. (After E. S. Goodrich, Lankester's 

 Treatise.) 



face, the Lepidosiren secretes a mass of mucus 

 round itself to prevent too great desiccation ; it 

 breathes entirely by means of its lungs, and awaits 

 the return of the rains to float it out of its cocoon. 

 As soon as the floods liberate it, Lepidosiren proceeds 

 directly to the duties of reproduction, and another, 

 though differently constructed, nest is built in the 

 mud below the water to receive the eggs and rear 

 the young. 



The habits of the African Lung-fish, Protopterus, 

 are very similar ; it too burrows in the mud on the 

 approach of the dry season ; but the Australian Lung- 

 fish, Ceratodus, appears to differ in this respect from 

 its two relatives. The air-breathing operations of 



