RESPIRATION IN WATER 



33 



Fig. 9. Gills of Salamandra larvae. 

 A, at 80 mm 2 tension and B, in pure 

 oxygen. (Drastich.) 



diffusion in air is about 1 million times more rapid than in the 

 tissue (p. 19). 



In several larval forms of fishes (Elasmobranchii, Polypterida, 

 Dipnoi) and Amphibia we find external gills in the form of 

 threads or fine feathers. Babak (1907) showed that the gills 

 which grow out in young 

 tadpoles of Rana temporaria 

 become large when the water 

 is poor in oxygen and rudi- 

 mentary when the water 

 is saturated with the gas. 

 Drastich (1925) made simi- 

 lar experiments on the larvae 

 of Salamandra. At a tension 

 of 80 mm the gills were much 

 larger and much more thin- 

 walled than at a tension of 750 mm (Fig. 9), but in spite of 

 the adaptation, metabolism was reduced and the growth 

 slower. 



The most remarkable development of functional gills is that 

 taking place in the male Lepidosiren during the period when the 

 fish attends to the eggs and young in the burrow constructed 

 for the purpose (Agar, 1908). Shortly before the mating, 

 filaments grow out on the pelvic fins which finally attain the 

 development shown in Fig. 10. Agar definitely states that 

 during this period the male remains in the nest and does not 

 come to the surface to breathe air, as it does regularly at all 

 other times. Cunningham (1929) and Cunningham and 

 Reid (1932) put forward the hypothesis that the male provides 

 oxygen for the eggs and young from his own blood through 

 these pelvic fin gills, because they assumed that the water in 

 the tropical swamps where Lepidosiren breeds is practically 

 2 -free. This assumption is no doubt correct regarding a 

 large part of the season, but certainly not just after the rains. 

 The Lepidosiren larvae themselves respire from the water by 

 means of external gills which begin to degenerate 45 days after 

 hatching (Carter and Beadle, 1930) and the larvae, which have 



