MARINE FOOD FISHES Ti9 
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-surmmer 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 
