Respiration 103 



respiratory in function. Those of mosquito and caddis-fly larvae 

 (Morgan QC O'Neil, 1931; Wigglesworth, 1933, a, b) appear to be 

 water-absorbing organs. 



Many animals that live in water must breathe air and will drown 

 if continually submerged and prevented from reaching the surface. 

 This is true of quite a number of species of fishes. Representatives 

 of some of these are able to wander over land at intervals and in 

 some cases to live for months or years out of water; others never 

 leave the water, and die quickly if they do so. Das (1927), Hen- 

 ninger (1907), Hora (1933), and others have studied tropical air- 

 breathing fishes which possess gills and special organs which are 

 adapted for breathing air gulped in from the surface. These fishes 

 die in from half an hour to four hours when immersed in water. 

 On the other hand, many animals that possess lungs for air-breath- 

 ing can live if those organs are removed. Krogh (1904) showed 

 that a frog can respire enough through its skin to live after its 

 lungs have been lost. Helff (1929, 1931) extirpated the lungs of 

 frog tadpoles and found that "the young frogs lived for three to 

 four weeks following complete metamorphosis." Yet he also dem- 

 onstrated that the lungs of tadpoles were functional for a consider- 

 able period prior to metamorphosis. The axolotl (Ambystoma larva) 

 survives after the removal of both lungs and gills, its skin being 

 adequate for all its respiration (Hogben, 1926) . Some amphibians 

 are peculiarly adapted to live without the lungs, which were doubt- 

 less characteristic of ancestral amphibians. Some highly aquatic 

 frogs have reduced lungs (Noble, 1925) ; salamanders of certain 

 species have no lungs whatever, and their respiration is through 

 enteric membranes and skin. In both these types of amphibians 

 there is a tendency toward the reduction of the heart from a 3-cham- 

 bered to a 2-chambered condition by the loss of the left auricle and 

 the loss of the spiral valve. In salamanders with lungs (Amby- 

 stoma) the development of lungs precedes that of the auricular 

 septum (Mekeel, 1930). Gage (1892) suggested that, in combin- 



