of the Fishery Board for Scotland. 



51 



The megrim or whiff is the only kind of fish I have met with that 

 exhibits a fairly constant difference in the shape of the right and leit 

 earstones. At first I imagined this difference to be merely accidental, 

 but the examination of several specimens, both large and small, revealed 

 similar differences in all of them. 



. The earstones of the argentine have also a peculiar shape, and are 

 unlike any of those that have been examined. They may be described as 

 scaphoid or boat-shaped, except that the length and depth are nearly the 

 same Two pairs of these earstones are represented on pi. i. b., figs. 44 

 and 45, and photographs of them considerably enlarged will be found on 

 pi. iv., fig. 9. 



The earstones of very young and immature fishes may, but frequently 

 do not, possess the characters peculiar to the species as seen in the adult 

 form, and it is this fact that makes the identification of fishes by the 

 earstones alone unsatisfactory, whereas if the fishes be of adult size, or 

 nearly so, the uncertainty of determination is greatly minimised. There 

 can, for example, be little or no difficulty in recognising the earstones of 

 adult whiting or codfish or of those of the hake. 



Besides the difference in the shape of the earstones of fishes there is 

 also sometimes considerable differences observed in the proportional sizes 

 of those of different fishes — that is, it does not always follow that a large 

 fish belonging to one species will have earstones proportionally larger 

 than a smaller fish belonging to another species, for we sometimes find 

 that the difference is the other way. For example, the earstones of a 

 lumpsucker fifteen and a half inches long measured l'5mm. by l*3mm.; 

 a lemon dab twelve inches long had earstones that measured 3*5mm. by 

 2mm., while those of a long rough dab ten inches long, or only two-thirds 

 the length of the lumpsucker, measured 6mm. by about 4'5mm — four 

 times the size of those of the lumpsucker. Then, again, a catfish, the 

 length of which was twenty-seven inches, possessed earstones 4mm. long 

 by 2'5mm. at the widest part, while a hake of about the same length as 

 the catfish was found to have earstones nearly 25mm. long by about 9mm. 

 at the widest part. Tn further contrast with the earstones of the fishes 

 just mentioned, it may be stated that a codfish measuring fully three feet 

 in length had earstones of about the same width as those of the hake, but 

 they were nearly 7mm. shorter, their length reaching only to 18mm., but 

 the difference in length was fully made up by their more massive struc- 

 ture. The weight of these two earstones was about 22 English grains, or, 

 more correctly, 1*485 grammes, while the weight of the two otoliths from 

 the hake was about 12 English grains, or -735 grammes. It may also be 

 mentioned that the two earstones of a codfish which measured forty inches 

 in length weighed nearly 30 English grains — and it should be noted that 

 this was the weight of them after they had been thoroughly dried. 



Moreover, the earstones of teleostean fishes appear to consist almost 

 entirely of calcareous matter, for when those from a tolerably large codfish 

 were subjected to a red heat they remained practically unaltered in size or in 

 shape, but were so brittle that they were easily crushed between the finger 

 and thumb. On the other hand, when otoliths were placed in dilute 

 hydrochloric acid they completely dissolved away with much effervescence, 

 leaving but the merest trace of organic matter. 



This calcareous matter does not form a homogeneous mass, but is 

 deposited in layers, and the density of each alternate layer is usually less 

 or greater than the one immediately preceding. In some cases these 

 layers are arranged so regularly as to imply a more or less regular and 

 periodic activity or quiescence in the secreting tissues by which the ear- 

 stones are formed. The result of this alternating activity and quiescence 



