128 TEXT-BOOK OF ZOOLOGY 



the great flexibility and elasticity of the vertebral column, owing to the 

 presence of thick cartilaginous plates (intervertebral cartilages) between 

 each two vertebrae. 



6. The whale, like all mammals, breathes the free atmospheric air 

 (not like fish, the air dissolved in the water). For the purpose of 

 breathing it rises to the surface every ten to fifteen minutes, though 

 wounded animals can remain below the water an hour and more. On 

 rising to the surface to breathe, the whale expels the used-up air through 

 the nostrils, with a noise audible for a considerable distance. Owing to 

 the cold in these latitudes, the water vapour with which this air is 

 saturated becomes visible (like the vapour of our breath in winter), and 

 appears in the form of two huge jets of steam ejected from the head 

 of the animal. It is this phenomenon which is spoken of as the 

 "blowing" or " spouting" of the whale. (The whale does not eject a 

 column of water like a fountain ; why not ? See Section 7, e.) 



(a) Being obliged periodically to come to the surface, and the body 

 of the whale being specifically heavier than water, there must be some 

 mechanism for driving it upwards. This is provided by the powerful 

 tail-fin, which accordingly has a horizontal position. (See Section 5, d.) 



(b) The nostrils are placed on the summit of a roundish prominence 

 on the top of the head, by which breathing is facilitated. Since the npse 

 is in mammals adapted for smelling in the air, it is not surprising to find 

 the olfactory nerve considerably atrophied in the whale. 



(c) The nostrils form narrow slits. Their walls lie very close together, 

 and the openings are closed by the pressure of the water when the 

 animal dives, so that no water can enter through them. In breathing 

 they are widely open. 



(d) The remarkably large lungs take up an immense quantity of air, 

 the animal requiring to respire only at long intervals. 



7. Food. — The Greenland whale is carnivorous. It is impossible to 

 estimate the quantity of food consumed by so colossal a creature. Only 

 the sea, with its superabundance of animal life, can supply its demands. 

 Owing to 



(a) The remarkably small calibre of the oesophagus, it is not capable 

 of swallowing a fish larger than a herring, The food can accordingly 

 consist of only small creatures. The native seas of the whale, in fact, 

 teem at or near the surface, especially at the border of the drift ice, with 

 myriads of small creatures, called by the whalers " whale-food." These 

 innumerable shoals consist principally of an almost transparent Pteropod 

 mollusc (Clio borealis), about 1£ inches long. These are associated with 

 equally large hosts of Amphipods from § to f inch in length. (Some 

 of these occur in our waters, e.g., the common " fresh-water shrimp"" 



