Whence the Shadows? 233 



Some sharks apparently are also capable of regurgitating what they 

 don't want, and also preserving for some time what they do. A 14-foot 

 Tiger shark that died in captivity in Australia was found to have in its 

 stomach two intact Dolphin-fish {Coryphaeiia) about 4 feet long. The 

 shark had been captured about a month before, and had been fed only 

 horseflesh, so it had managed to keep the dolphins preserved for at least 

 a month. Thirty-two fish, averaging 15 inches in length, were found 

 packed— and undigested— in a 13-foot Tiger shark, also captured in Aus- 

 tralia, 



A primitive form of alimentary anatomy, called the spiral-valve in- 

 testine, possibly is the answer to how the shark is able to disintegrate 

 horseshoes and to store dolphins, all in the same stomach. The simple 

 digestive tract of the shark is shaped like a lazy Z. The food enters the 

 mouth at the left end of the upper bar of the Z. From that point to just 

 about the left end of the lower bar of the Z is the stomach, in which little 

 digestive action takes place. The stomach seems, thus, to be little more 

 than a storage pouch. But, as the food begins the last leg of its trip, 

 along the lower bar of the Z, it enters the intestine, where the digestive 

 process starts in earnest. 



In the earliest vertebrates, the stomach was where food was sorted 

 and the intestine was where food was broken down into simple sub- 

 stances that could be absorbed by the intestinal wall for circulation to 

 body cells. Essentially, this primitive system is still present in the shark. 

 The higher vertebrates, including man, have developed a convoluted 

 intestine so that food passing through it can be exposed to as much 

 intestinal wall as possible in a small area. The shark's intestine is a cigar- 

 shaped tube. Food would sweep down it, with little chance for digestive 

 action— except for the fact that inside the tube is the spiral valve. 



The spiral valve is something like a carpenter's auger. The food 

 spirals down it and thus its exposure to the surface area in the gut is 

 greatly increased. The end-products of this spiraling process are spiraled 

 faeces. A4illions of years ago, ancient sharks also dropped such oddly 

 shaped dregs. They were fossilized and became prehistoric curios that 

 palaeontologists today call coprolites; a word meaning, literally, dung 

 that has turned to stone, and which is used for any fossilized faecal 

 matter. 



Dr. Eugenie Clark, whose continuing research has produced many 

 new facts about sharks, has proved that sharks can be trained. Prior to 

 her recent experiments, little was known about the shark's capacity for 

 learning, and the assumption was that the shark was of a low order of 

 intelligence. 



Dr. Clark trained a male and a female Lemon shark (Negaprion 

 brevirostris) which had been in captivity for 4 months. They were kept 

 in a pen near her laboratory dock. When the training began, pieces of 



