66 COD; HADDOCK, ETC. PLEUB,ON 7 ECTID.E, OR FLAT FISH. 



of the ground on which it is taken. Their reproductive powers are 

 enormous ; the roe of a single female having been estimated to 

 contain nine millions of eggs. Nearly allied to the Cod, are the 

 Haddock, Whiting, Hake, Ling, Rockling, Coal-fish, and others. 

 The first of these is considered as the most delicate of the whole 

 family, when fresh ; but it does not take salt well ; and for pre- 

 servation, the Cod and Ling excel the rest. The Burbot, or Eel- 

 pout, a fish nearly allied to the Ling, inhabits the rivers and lakes 

 of some parts of Europe and Asia. It is found in some English 

 rivers. 



628. The second family consists of the PLEURONECTID.E, or 

 Flat-fish. These present several remarkable peculiarities of 

 structure ; by which they are distinguished, not only from all 

 other Fishes, but even from all other Vertebrated animals. 

 Their body is extremely compressed, or flattened at the sides; 

 the animal, however, does not habitually swim with these sides 

 erect in the water, but usually lies flat on the bottom, one side 

 being in contact with it, and the other being directed upwards. 

 The lower side is generally white, whilst the upper is brown ; 

 and the former is commonly (but erroneously) regarded as the 

 belly of the fish, and the latter as its back. The dark colour of 

 the upper surface harmonises with that of the bed on which the 

 fish lie ; so as to enable them to conceal themselves from their 

 foes, or to watch for their prey, without being themselves ob- 

 served. Individuals are occasionally met with, in which both 

 sides are coloured alike ; these are said to be " Doubles." It is 

 usually the coloured side which is doubled ; though it is occa- 

 sionally the white one. By a change in the position of the 

 head, both the eyes are brought round to the right side, so as to 

 look upwards, when the fish is lying on the bottom ; this change 

 may be designated as a sort of twisting round ; but it also in- 

 volves an unequal development of the bones on the two sides of 

 the head, which shows itself in the mouth. Of the pectoral fins, 

 too, one is usually larger than the other. The dorsal fin is con- 

 tinued along the whole of the ridge of the back, from the head 

 to the tail ; and the anal fin usually forms a like continuous ex- 

 pansion below, sometimes uniting with the ventral fins. The 



