MARINE FOOD FISHES 119 



the cranial cavity and an otolith will be found on the 

 right and left side. 



In the illustrations of four otoliths facing p. 118 

 the two top photographs are of otoliths removed from 

 a group of plaice fourteen and a half inches in length, 

 and show a central white portion which indicates the 

 first year's spring-summer growth of the fish. Then 

 follow four white rings indicating that the fish in this 

 group were five years old. The two lower otoliths were 

 fish from the second group, measuring about eighteen 

 inches in length. These fish were the next in size and 

 a year older, and the otoliths show an additional white 

 ring. 



The method of colour protection in flat fishes has 

 already been briefly referred to. Reflection plays very 

 little part in the concealment of flat fishes, for they 

 depend on becoming light or dark to suit the general 

 tone of their surroundings by the contraction or relaxa- 

 tion of existing colour cells. The variation in the mark- 

 ings and colour of young flat fishes is very great. 



The expert can recognise the tiny plaice, sole, lemon- 

 sole or flounder by their shape, but it may be useful to 

 the uninitiated to remember that if a finger is run 

 along the upper surface of the fish from the tail to the 

 head, the plaice feels quite smooth, the sole rough, and 

 the flounder rough only along the centre line. 



Of round food fishes we have already referred to the 

 cod family, another important group is to be found in 

 the herrings, which include the herring, the sprat, the 



