292 TEXT-BOOK OF ZOOLOGY 



Tunny and Flying-Fish. 



The Tunny (Thynnus thynnus) is to the coast - dwellers of the 

 Mediterranean what the cod is to the inhabitants of the North Sea 

 (which see). It reaches a length of about 13 feet, and a weight of 

 several hundred pounds. The upper side is of bluish-green colour, the 

 under surface grey with silvery spots. On the tapering tail several 

 supplementary fins are found between the second dorsal and the anal 

 fins on the one side, and the crescent-shaped caudal fin on the other. In 

 the spring the tunny approaches the coast in enormous shoals for the 

 purpose of spawning (see herring). It is caught in different ways in 

 different localities : in some places with hooks or harpoons, in others in 

 seines or set-nets. The fishery is specially productive on the coasts of 

 Sicily and Sardinia. Here large stationary nets forming several com- 

 partments are arranged and moored in the shallow water along the coast, 

 and into these the fish can enter, but cannot escape. When a sufficient 

 number of fish have been trapped in the last compartment, known as the 

 " death chamber," a terrible slaughter of the captives is commenced. 

 The flesh is not eaten fresh, but is dried or salted: It spoils, however, 

 very easily, and is then very poisonous. 



Among the numerous species of fish which are able temporarily to 

 leave their native element, the water, the best known is the Flying- 

 Fish (Exocoetus evolans). In appearance it resembles a herring, but the 

 pectoral fins are of great size and have the form of wings. When 

 pursued by one of its numerous enemies, it leaps with great force out of 

 the water, and, using its fins like a parachute, soars for stretches of about 

 600 feet over the waves. It inhabits the seas of the warm and temperate 

 zones. 



The Common Plaice (Pleuronectes platessa). 



(Length from 12 to 30 inches.) 



The adult plaice is a vertebrate animal with a strongly asym- 

 metrical body. This deviation from the normal shape (see Part I., 

 pp. 1, 2) becomes, however, explicable from a closer study of its mode 

 of life as a bottom fish. The young plaice have a symmetrical shape 

 exactly like other fish ; they swim in the same manner, and have both 

 sides of the body of the same colour. As they grow larger the body 

 increases vertically in height, and the fish more and more frequently and 

 for longer periods lie on their left side, which the full-grown fish turns 

 towards the sea-bottom throughout the rest of its life. In this position, 

 however, the left eye of the fish would be useless for sight, which would be 



