RESPIRATION IN WATER 



41 



increase is due to the w.ork of the respiration muscles. In air 

 breathing forms the cost of increased ventilation is much 

 smaller (p. 68). 



There can be little doubt that fishes swimming rapidly do 

 not make respiratory movements at all, but obtain the neces- 

 sary ventilation of the gills simply by opening the mouth. 

 Certain fishes, of which the mackerel (Baglioni, 1910; F. G. 

 Hall, 1930) is the best-known example, are constant swimmers 





sa 



tfttfffifffj 



FIG. 3 



FIG. 4 



Fig. 17. 7. Portion of gill arch in Esox with filaments attached. Magni- 

 fication about 6/1. 2. Similar view from Amia. 3. Section through two gill 

 filaments of Esox. Ca. 65/1. 4. Similar section from Amia with central sup- 

 porting bar C.S.B. Ca. 65 1. (Bevelander.) 



and have lost the power of ordinary respiration. They cannot 

 therefore be kept in aquaria, but only in ring-shaped or very 

 large basins. 



G. Bevelander (1931) describes a very peculiar gill structure 

 observed in Amia calva, shown together with that of the pike 

 in Fig. 17. The lamellae of the filaments are joined together 

 so that the whole is honeycombed, and large and very thin- 

 walled capillary surfaces are exposed to the water. This may, 



