232 Shark and Compajjy 



severed, the shark showed no response to movements in the water. This 

 also indicates that the lateral line has something to do with balance. 



Although the functions of the lateral line are not fully understood, 

 experiments such as Wisby's may prove the theory that the lateral line 

 is a sense of "distant touch," a kind of signal receiver which can trans- 

 late distant vibrations into meaningful messages to the brain. Subtle move- 

 ments in the water far from a shark send out feeble vibrations that travel 

 through the sea at about 5,000 feet a second. It may be that the lateral 

 line picks up such vibrations, and, through some process, the shark 

 "reads" the vibrations as, say, waves lapping a shore— or the swimming 

 pattern of a potential meal. 



In addition to the lateral line, most sharks, skates, and rays possess an- 

 other curious sense system, which appears as a number of pores— some- 

 times several hundred of them— scattered about the head. Each of these 

 pores forms one end of a tube whose other end consists of a group of 

 sensory cells called Lorenzini's ampullae, after the man who first de- 

 scribed these odd sense organs in 1678. The word ampullae derives from 

 their shape, which is similar to an ampulla, a narrow-necked bottle the 

 Romans used in anointing themselves after bathing. To the modem eye, 

 ampullae look like Coke bottles. Each ampulla is filled with a jelly-like 

 substance that appears to react to either pressure changes or temperature 

 fluctuations, or possibly both. 



Scenting, seeing, sensing the slightest signal from pressures, vibra- 

 tions, and temperatures in its watery kingdom, the shark is like a com- 

 puter constantly at work on a single equation: Life = Food. Sharks 

 do not always eat, and they do not devour all the food they see. Skin- 

 divers have seen sharks swimming through schools of fish without mo- 

 lesting them. But, in the hungry sea, the brain of a shark undoubtedly 

 does not dwell for long on thoughts other than food. 



Every shark is carnivorous, whether its prey be microscopic plankton 

 or the giant sea turtle. Many sharks are gastronomically uninhibited. 

 And their admirably stalwart digestive system apparently can take any- 

 thing the shark happens to eat. Abundant amounts of gastric juices, 

 liberally laced with hydrochloric acid, speedily break down edibles, and 

 the speed of the process may account for the ravenous hunger of most 

 sharks. In the opinion of some authorities, the digestive juices— strong 

 enough to burn the varnish off a deck— can eventually dissolve even 

 metallic objects the shark gulps down. 



The Selachians have strange stomachs in keeping with their often 

 strange diet. In some, and perhaps many or all species, the stomach is 

 extensible, and it may be capable of turning inside out and everting, so 

 that it extends beyond the jaws. (Inside-out stomachs occur when dead 

 sharks are hung up by their tails, but it is not definitely known whether 

 any live shark is capable of voluntarily inverting its stomach.) 



