456 ANIMAL RESPIRATION 



perfectly lively and at their ease, and not in the least disturbed by 

 finding themselves among these most unsanitary surroundings. 

 This is the occasion when Ceratodus enjoys the advantage of 

 its lungs. Not on land, not during a summer sleep in the mire 

 or in a cocoon are they most serviceable, but in an extremity of 

 this kind, when they furnish the only means by which the fish 

 manages to outlive the most unfavourable conditions of its native 

 rivers." 



The African Lung- Fish i^Protopterus), specially abundant in the 

 basins of the White Nile and Congo, is more specialized than its 

 Australian congener, and its swim-bladder is modified into a 

 double lung with spongy wall. It is commonly found living in 

 swamps or shallow streams which practically disappear during the 

 dry season, and spends that part of the year in a torpid condition 

 (summer sleep), imbedded in the mud, and surrounded by a sort 

 of capsule or cocoon formed by the hardening of slime secreted 

 by its skin. In this state, it is said, the natives dig it out for 

 food, and dormant specimens of the kind have been transported 

 to Europe, surrounded by the capsule and a mass of hardened 

 clay. When placed in warm water these investments readily 

 break down, and the fishes thus released are none the worse for 

 their long journey. The newly-hatched Mud- Fish possesses not 

 only internal gills, but also long, plume-like external gills (like 

 those of a tadpole), which persist in the adult, though in a reduced 

 state. 



The American Lung- Fish {Lepidosireii), native to the basins 

 of the Amazons and Paraguay Rivers, closely resembles the Afri- 

 can form in the structure of its breathing organs and in its habits. 

 Prof Graham Kerr has shown that, during the egg-laying season, 

 numerous scarlet filaments grow out from the pelvic fins of the 

 male in a feather-like way, and he considers these to be acces- 

 sory breathing organs. 



AMPHIBIANS (Amphibia) 



Certain Tailed Amphibians {Urodela) are amphibious in the 

 adult condition, possessing a pair of simple lungs, and also gills. 

 This is the case with some of the Salamanders, creatures which 

 may be regarded as first cousins of the Newts or Efts which 

 abound in many of our ponds and ditches. In the Hell- Bender 



