22 GIANT FISHES 



rakers, each of which is from 4 to 6 inches long, are closely 

 set in a row on each gill-arch, and, as they project across the 

 internal clefts leading into the gullet, they form a very effective 

 sieve or strainer. Their microscopic structure is very similar 

 to that of the teeth. In appearance they recall the baleen 

 plates of the whalebone whales (see p. 203), and have an 

 exactly similar function. Indeed, they provide an excellent 

 example of what is known to scientific men as parallelism : 

 that is to say, the evolution in totally unrelated groups of 

 animals of similar structures designed to serve the same ends. 

 It was the fancied resemblance of the gill-rakers to the whale- 

 bone plates that led the older whalemen to call this shark the 

 " Bone Shark ", a name still in use in some parts of the world. 

 A study of the normal food of the Basking Shark gives a clue 

 to the meaning of these structures. The diet consists almost 

 entirely of small shrimp-like crustaceans, together with other 

 minute creatures that swarm near the surface of the sea and 

 make up what is known as the plankton. The manner of 

 feeding is simplicity itself, and the Basking Shark has no call 

 to go in active pursuit of its prey like its fish-eating rela- 

 tives. Swimming among a mass of plankton, with its large 

 mouth wide open, the shark takes in quantities of water with 

 the contained life. This water is forced out through the gill- 

 clefts, leaving the food adhering to the inner walls of the gullet 

 and to the sieve-like gill-rakers, where it can be swallowed 

 at leisure. The water which passes over the gills serves to 

 oxygenate the blood, so that the Basking Shark may be said 

 to feed and breathe by one and the same action ! 



Nothing is known of the breeding habits of the Basking 

 Shark, but it is assumed to be viviparous like the other members 

 of the family. Very young specimens have never been seen, 

 and it is probable that these stay in deep water until they grow 

 to a fair size. Small individuals, 10 to 15 feet in length, 

 are sometimes captured, however, and differ markedly from 

 the adults in the shape of the head. The fore part of the 

 head is considerably drawn out, and forms a thick, pointed, 

 fleshy snout, the tip of which is produced into a curved, 

 soft hook. 



The flesh is of little value as food, and the Basking Shark 

 cannot lay claim nowadays to be of much economic value. 



