Fishes (Pisces). lo^ 



come very important in scientific research, and zoologists have 

 drawn largely upon the material which this Aquarium provides. 

 Economically, however, the Dog-fish is of very little use. Its flesh 

 is of indifferent quality and only eaten by the poor; the skin 

 (shagreen) is used for polishing, and the liver yields a certain 

 amount of oil. Almost all sharks are viviparous, so that Scy Ilium 

 is an exception to the rule. 



The Smouth Hound or Ray-toothed Shark, Mustelus (fig. 59), 

 is only rarely to be seen in the Aquarium. This is one of the most 

 harmless of sharks; its blunt flat-topped teeth are not fitted 

 for devouring anything but crabs and mollusks, which it captures 

 at great depths. When placed in tank Nr. 10, it swims about at 

 first in a very lively manner with most graceful movements of 

 its glossy body, but it soon tires, and finally cannot lift itself 

 from the bottom of the tank; nor will it touch any food in captivity. 

 Its flesh is quite good eating. 



The Angel-fish or Squatina (fig. 61), which forms a connecting 

 link between the Sharks and the Rays, is an unsightly beast. 

 It must have come by its name in the well-known way: lucus a 

 non lucendo, for its characteristics are far from angelic. It is 

 ugly, stupid, lazy and greedy possessing these qualities to a 

 greater degree than almost any other fish. The big uncouth 

 beast rests always on the bottom (being often taken for dead), 

 half hidden in the mud, lying in wait for other animals which 

 it swallows unchewed. If they are too large it swallows them 

 in jerks as more and more room is made in the stomach by diges- 

 tion. Its very indifferent flesh is eaten by poor people, its rough 

 skin is used for graters, sheaths for knives, and other purposes. 



The true Rays have a flat body compressed from above, which 

 has on its upper darker surface the eyes and two openings leading 

 to the gills. On the lower paler surface are situated the mouth, 

 the nasal aperture and the gill-slits. They are typical bottom- 

 fish and feed on other ground-animals. 



The most interesting of these fishes is the Electric Ray (Torpedo, 

 fig. 64), which was known to the ancients for its strange power 

 of giving electric shocks. Its slimy body is almost circular in 

 shape and contains two large "electric organs". Each of these 

 consists of several hundreds of hexagonal columns of a gelatinous 

 substance, which are supplied by a number of branching nerves 

 with curious terminations. These organs give rise to a strong 

 electric current when the animal is irritated; this can be demon- 

 strated with a telephone or a small electric lamp which glows at 

 every discharge. 



To experience the whole shock, the fish must be touched at 

 the same time on both sides. The shock is not so strong as that 

 of the South American Electric Eel, but is still sufficiently painful 

 in an adult Ray. The shocks become feebler when repeated fre- 



