102 



WHALES 



Figure jg. A Humpback' s somersaults after a sketch by Batman and Hermans of an 

 observation made ojf East Australia in 1955. 



hence to exert a continual thrust in a forward direction (Fig. 63). The 

 effects of the tail's vertical motions naturally cancel out, so that this forward 

 thrust determines the propulsion. (The same principle operates in fish, 

 though here the tail is waved in a horizontal plane.) The peduncle of the 

 tail may even be said to have a braking effect, but the latter is negligible 

 since the tail is not only streamlined but so laterally compressed, that it 

 cuts through the water very much like a knife. The reader might wonder 

 how so relatively small a part of the whale as the flukes can manage to 

 propel the animal's gigantic bulk, but he need only think of a large ship's 

 small screw to lealize that mere size is unimportant. Woodcock (1948) 

 observed that dolphins accompanying a ship at 20 knots beat their tails at 

 a rate of two beats per second, while Gunther (1949) measured 1-2 beats 

 per second in the case of a Fin Whale making 10-12 knots. 



Even though the whale is thus propelled as a result of its tail's vertical 

 beat, the tail can also bend horizontally. However, here there is no special 

 'fulcrum' at the base of the flukes. The lateral motion is undoubtedly 

 needed for steering and particularly for quick turns, in short for most of 

 the animal's aquatic feats. The flippers contribute a small share to the 

 steering effect and particularly help to balance the animal on its course, 

 and the dorsal fin also plays a part as a stabilizer, though stability, as we 

 have seen, is primarily assured by the high-up position of the lungs. 



We have also seen that the trunk in Cetaceans is fairly rigid, and the 

 typical curved appearance of the back when the animal is surfacing is 

 mainly due to the fact that head and tail are bent down. Oddly enough, 

 while Cetaceans have a very short and rigid neck, the head of some 

 species, e.g. Bottlenose Dolphins and Boutus, can make an angle of 45° 

 up or down with the trunk, and somewhat smaller angles in a lateral 

 direction. However, the head is not equally movable in all species, and 

 that of the Pilot Whale is particularly immobile. This may well be due to 

 the fact that its food consists exclusively of cuttlefish which, on the whole, 

 are not as mobile as fishes. Since the neck is fairly rigid in most species, 

 the head is moved by the joint between the atlas (the first cervical 

 vertebra) and the occipital bones at the rear of the skull. This joint which 



