DOLPHINS AND SIRENS. 45 



The teeth are modified in accordance with the task 

 which they have to perform. They are very nume- 

 rous, some forty or fifty on each side, and are so 

 arranged that when the jaw is closed, they interlock 

 with each other. This is needful, on account of 

 the nature of their prey. The fish on which it 

 feeds are not only active; but, as a rule, are de- 

 fended with a scaly armour, which would enable 

 them to slip out of the grasp of a mouth less formid- 

 ably armed. 



The teeth are rather long, sharply pointed, and 

 are all alike; there being no distinction between 

 incisors, canines, and molars. If a section is made 

 of them, they are seen to be hollow cones, supplied 

 with fresh substance of a soft pulp which fills the 

 interior. They are exceedingly variable in number, 

 some falling off in front, while others are developed 

 behind, their number apparently depending on the 

 size of the jaw. 



One main point in the economy of the Porpoise is 

 the flexibility of the body. This is absolutely neces- 

 sary in order to enable the animal to turn and twist 

 in the water with sufficient activity to take its prey. 

 Sometimes it is able to come upon a shoal of herrings, 

 pilchard, mackerel, or other fish ; and works frightful 

 havoc among them, driving into the shoal, and 

 snapping up the fish as they are crowded together 

 and hampered in their movements. But these are 

 exceptional pieces of good fortune ; and when the 

 Porpoise has to match itself against such a fish as a 

 salmon, it needs agility as well as speed ; and those 

 who have seen it while engaged in salmon hunting, 



