52 Part III —Twenty-fourth Annual Report 
is well seen in the structure of the otoliths of several species of the 
Pleuronectide, the shape, of which is more or less circular, and they are 
so thin as to be almost transparent, especially when just removed from the 
ear-chamber. It is evident that the calcareous matter that is added 
to these earstones from time to time is deposited chiefly around the 
circumference, and only to a small extent laterally. In several of the 
Gadide, on the other hand, considerable additions are made to the thick- 
ness as well as round the edges of the otoliths. In not a few other fishes 
‘the form of the earstones is so irregular that the calcareous matter of 
which they are composed cannot have been added symmetrically as in the 
ease of the earstones of the Pleuronectide. 
An attempt is being made to utilise these concentric growth-lines for 
the purpose of ascertaining the age of the fish they belong to, somewhat 
after the manner a botanist reckons the age of an exogenous tree by 
counting the number of alternating light and dark rings exhibited in a 
cross section of the wood; and it is probable that an estimate of the fish’s 
age founded on these growth-lines may be approximately correct as regards 
plaice or any other fish whose earstones have a regular form and are 
sufficiently thin to show the concentric lines clearly. But it is doubtful 
how far such a method can be relied upon if applied to such fish as the 
bream, mullet, hake, herring, and others having earstones irregular in 
shape. Moreover, it is probable that the abundance or scarcity of food 
that the fish have to live upon, or variations in the kinds of the food, may 
retard or quicken the deposition of calcareous matter, and may lead to the 
formation of pseudo rings, whole or incomplete, that may tend to com- 
plicate or in some measure to nullify the calculation. 
The discussion of these questions is, however, outside the scope of the 
present paper, which is merely intended to contain notes descriptive of 
the sizes and forms of the earstones of a number of the fishes that have 
come under my own observation. 
The plates which illustrate this paper were prepared from photographs 
wade by my son, Andrew Scott, A.L.S. The earstones represented by 
the photographs were collected at various times and mounted on slides, 
by myself, but only a limited number of them were selected for 
mounting. Those represented on Plates I., II., and III. are nearly twice 
the natural size, while Plates IV. and V. show them considerably 
enlarged. 
II.—LIST OF FISHES WHOSE EARSTONES ARE DESCRIBED IN THE 
PRECEDING NOTES—ALPHABETICALLY ARRANGED. 
PAGE 
Agonus cataphractus (Linn.), Pogge,  - = : : < at WBE 
Ammodytes tobianws, Linn., Lesser sand-eel, - : 2 5 2 5269 
Anarrhichas lupus, Linn., Catfish, - - : < : EG 
Anguilla vulgaris, Leach, Fresh-water eel, — - - 2 = 79 
Argentina sphyrena, Linn., Argentine, : - : : 7G 
Atherina presbyter, Cuv., Sand smelt, - - - - - =". 460 
Bothus maximus (Linn.), Turbot, - = = s . eee 7 ( 
Callionymus lyra, Linn., Dragonet, - = : = oy 358 
maculatus, Bonepart, Spotted dragonet, - : Bill G33 
Clupea harengus, Linn., Herring, = : z re 
»,  pilchardus, Bloch., Pilchard, - . = : : eas 
»  sprattus, Linn., Sprat, - - = - = : 1 278 
Conger niger (Risso), Conger-eel, - : - - = Fe) 
Coregonus lavaretus, Penn., Powan, - - E - = is 
Cottus scorpzus, Linn., Sea scorpion, - : : 2 = S55 
Cyclopterus lumpus, Linn. ., Lumpsucker, = : - ea) 
Drepanopsetia platessoides (Fabr.), Long rough dab; = S a ae (RE) 
Enchelyopus viviparus (Linn.), Viviparous blenny; - : - (50) 
Esox luctus, Linn., Fresh-water pike, - : < 77 
