52 



Part III. — 1 'went y-fou rth Annual Report 



is well seen in the structure of the otoliths of several species of the 

 Pleumnectidse, 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 

 Gadidse, 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 

 case of the earstones of the Pleuronectidse. 



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 

 made 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. 



A yonus cataphractus (Linn.), Pogge, - - - - - - 56 



Ammodytes tobianus, Linn., Lesser sand-eel, - - - - - 69 



AnarrJiichas lupus, Linn., Catfish, - - - - - - 59 



Anguilla vulgaris, Leach, Fresh- water eel, - - - - - 79 



Argentina sphyraina, Linn., Argentine, - - - - - 76 



Athtrina presbyter, Cuv., Sand smelt, - - - - - - 60 



Bothus maximus (Linn. ), Turbot, - - - - - - 70 



Gallionymus lyra, Linn., Dragonet, - - - - - - 58 



,, maculatus, Bonepart, Spotted dragonet, - - - 58 



Clupea harengus, Linn., Herring, - - - - - - 77 



,, pilchardus, Bloch., Pilchard, - - - - - - 78 



,, sprattus, Linn., Sprat, - - - - - - - 78 



Conger niger (Risso), Conger-eel, - - - - - - 79 



Coregonus lavaretus, Penn., Powan, - - - - . - 76 



Cottus scwpius, Linn., Sea scorpion, - - - - - - 55 



Gydopterus lumpus, Linn., Lumpsucker, - - - - - 59 



Drepanopsetta platessoides (Fabr. ), Long rough dab, - - - 69 



Enchelyopus viviparus (Linn.), Viviparous blenny, - - - - 60 



Esox lucius, Linn., Fresh- water pike, - 77 



