216 



Comparative Animal Physiology 



the rate at which the water passes over them, and in the mackerel, for instance, 

 respiration is inadequate to support life unless the fish is in constant forward 

 motion. i'^-' It is essential that the mackerel keep moving! Teleost gills are 

 capable of independent but coordinated movement, and Bijtel'^^ has observed 

 in windowed specimens a mechanism by which fish gills close the gaps at their 

 tips, thereby impeding water flow during the "coughing" reflexes apparently 

 associated with cleaning out the gill passages. The gills of Amphibia-func- 

 tional throughout the lifetime of some urodeles and only during the larval 



B 



D 



Fig. 38. Gill filaments of larval Salamandra. Schematic representation of gill filaments 

 of larvae raised under conditions of (A) low oxygen tension (80 mm. Hg) and (B) 

 high oxygen pressure (760 mm.Hg). Transverse sections of filaments of larvae developed 

 in (C) low and (D) high oxygen tensions. From Drastich."* 



Stage of others, but always supplemented functionally by cutaneous or lung 

 ■respiration— may show modifications in size and arborization within single 

 individuals in response to changes in the availability of oxygen. The gill fila- 

 ments of larval Salamandra, for example, are large, branched, and thin-walled 

 on animals raised in low oxygen tensions (80 mm. Hg), but on salamanders 

 developed at high oxygen pressure (760 mm. Hg) they are small, stubby, and 

 thick-walled»8 (Fig. 38).'' 



Boell (personal communication) reports no decrease in oxygen consumption by 

 Amhlystoma deprived of gills. 



