Whence the Shadows? Ill 



the head-down suspension seems to have some effect on its nervous sys- 

 tem. Some experts believe that the shark's primitive nervous system 

 may be damaged by fright alone, a reaction animal behaviorists think 

 they have detected in some mammals. 



A sports fisherman tells of catching a shark, removing its liver for 

 chum, and then tossing the shark back into the sea as so much offal. The 

 shark swam away, showing no apparent ill effects. A Dogfish (Mustelus 

 canis) captured in Buzzards Bay, Massachusetts, had a large hole through 

 the wall of its body. The wound had been plugged by a lobe of the liver 

 which had simply grown into the hole! 



Stories are many of sharks' struggles against death and their apparent 

 insensitivity to what in other creatures would be intense pain. But a 

 headless, disemboweled shark writhing on a beach is not really strug- 

 gling against death. Rather, its biologically simple body is throbbing with 

 reflex actions. It is death that is doing the struggling, for snuffing out 

 such a vibrant, basic form of life takes a long time. 



All evidence points to the behef that pain, as we know it, does not 

 exist for Selachians— or fishes in general— or at least they have a very 

 high pain-threshold. In man, the sensation of pain originates in certain 

 nerve receptors that transmit impulses to the higher evolved nerve cen- 

 ters of the brain. Presumably, the lower a creature on the evolutionary 

 scale— and Selachians are well down it— the less developed is its sense 

 of pain. 



The shark's tenacity of life begins at the moment of birth, when it 

 emerges from its mother or its egg-case as a miniature replica of its el- 

 ders: voraciously hungry, ceaselessly moving. Day-old pups, as shark 

 young are called, have been seen going for baited hooks. Two of the au- 

 thors have seen captured sharks give birth to pups that skittered across 

 the deck of a boat, wriggled through the scuppers or leaped over the gun- 

 wale and plunged into the sea— to begin a swim that would end only 

 when they died. For, though sharks can rest on the bottom, they lack 

 the swim bladders that give buoyancy to the Teleosts. 



This lack of a swim bladder (or, as it is sometimes called, air bladder) 

 makes it impossible for the shark to maintain an equilibrium of depth. 

 Its body is more dense than the water it displaces and will sink to the 

 bottom unless sustained by constant motion. The shark, then, is con- 

 stantly striving to keep itself from sinking. Only bv a continual un- 

 dulation of its muscular tail and, to some extent, its fins, can the shark 

 overcome the gravity that inexorably pulls it downward. Unlike the 

 typical Teleost fishes which lie bloated in death on the surface of the 

 sea, when the shark can swim no more its body settles to the oblivion of 

 the deep. 



However, at least one species, the Sand Tiger shark {Carcharias 



