144 



WHALES 



Figure 83. Top: Photograph 

 of a microscopic preparation of 

 the lung oj a Bottlenose Dol- 

 phin, showing longitudinal- 

 section of bronchiole with 

 cartilage and annular muscles. 

 Photograph : W. L. van 

 Utrecht of a preparation made 

 by Miss J. R. Goudappel, 

 Amsterdam. 



Bottom : Longitudinal and 

 cross-section of a bronchiole of 

 a dolphin showing system of 

 annular muscles in the walls. 

 Annular muscle fibres = Af; 

 circular and radial elastic 

 fibres = Ef; cartilage = C, 

 surrounded by longitudinal 

 elastic fibres (Ef). 



' -O 7/ 



.mi^:^^^ ^^ 



^Af 



in the alveoli, however, that the air is most needed, as essential gaseous 

 exchanges take place in them, the alveoli must be shut off from the rest of 

 the respiratory system by a kind of tap, or else the animal could not make 

 full use of the air it has taken down. 



But why is there a system of successive taps instead of a single one? The 

 best person to answer this question is your plumber, who will tell you 

 straight away that it is unsafe to regulate great water pressures by means 

 of a single stop-cock, as the water would gush out far too forcefully. Only 



