THE AGE OF FISHES AND THE RATE AT WHICH THEY GROW. 409 
By examining large samples these exceptional instances cease to have 
any importance, as they are not sufficiently numerous to alter the average 
values obtained. 
The Salmon is one of the fish the age of which is often well shown on 
the scale, and a good deal of work has been done upon it (Masterman, 18). 
The Herring is another case which I shall consider in more detail 
presently. 
In certain other fishes, as for example the Plaice, the scales, although 
they show indications of similar winter rings, are not marked sufficiently 
clearly to make them easily available for age determination. Fortunately, 
however, other structures of the fish have been found which show in a 
very definite way alternating rings expressing different rates of growth, 
which enable us to estimate age with great accuracy. These structures 
are (1) the otoliths or ear-stones, and (2) certain of the bones of the fish. 
In the Plaice, the fish to which this method has been chiefly apphed, the 
age of the younger fishes up to about six or seven years old is best seen 
on the otolith, that of older ones on the bones. 
The otoliths or ear-stones (Fig. 4) are small, oval, caleareous bodies 
which he in the cavity of the inner ear. They can be removed easily for 
Fic. 4.—Otoliths of mature male Plaice. Upper row—Otoliths of Plaice from 
the West Bay (English Channel). Lower row—Otoliths of Plaice taken in 
the southern deep water of the North Sea, uear the Gabbard Light Vessel. 
(After Wallace. ) 
examination from the dead fish by making a single incision in the head 
in an appropriate direction, and an inspection with a simple lens generally 
suffices to make an age determination (cf. Reibisch, 21). 
As will be seen from the figure, alternate white and dark rings are seen, 
when the otolith is examined by reflected light. The white rings are 
