2o8 THE SEAS 



known as the gill-rakers (Plate 76) . These are best devel- 

 oped in the Basking shark, a tropical fish which spends its 

 life near the surface feeding on small animals. The bottom- 

 living fish, such as the flatfish and rays, live upon the 

 worms and shellfish of various kinds which they seize and 

 crush up with their powerful jaws. It is because the 

 Dogger Bank has an exceptionally rich fauna of bivalve 

 molluscs which are found in great patches sometimes 

 fifty miles by tw^enty, and at a density of between 1,000 

 and 8,000 per square metre, that the Bank forms such an 

 ideal region for the growth of plaice. The rays are often 

 able to crush up the massive shells of the larger bivalves 

 such as the oyster, one of their number forming the most 

 serious enemy of the pearl oyster on the Ceylon beds — 

 yet not an enemy to the pearl diver for this ray is the 

 second host of the tapeworm, the early stages of which 

 live in the pearl oyster and often form the nucleus round 

 which pearls are formed. Other rays do serious damage 

 to the deeper-water oysters ofif the eastern coast of North 

 America . More actively swimming fishes such as the cod and 

 haddock also feed on the bottom animals. Other fishes 

 pursue their small relatives ; the herring shoals for 

 'instance are invariably accompanied by great numbers 

 of dog-fish which annually devour large numbers of herring. 

 More unique are the feeding habits of the Angler, a sluggish 

 fish which lives on the sea bottom and has a short stumpy 

 tail, a comparatively small body and an immense head 

 and broad mouth with inwardly pointed, hinged teeth. 

 Above the mouth is a slender spine, the modified first ray of 

 the dorsal fin, with a tufted end ; the Angler lies per- 

 fectly still with its huge mouth shut and daintily waving 

 this tentacle as a lure ; thus, far from having to hunt their 

 prey, fish of all kinds, impelled by curiosity or desire for 

 food, come to inspect the lure and are seized in a moment 



