of the Fishery Board for Scotland. 



L33 



order to grind the other surface. After the operation the .section is 

 opaque from the scratching of the surface, and if it is clarified and 

 mounted in balsam it becomes too transparent, so that the contrast 

 between the opaque and transparent zones is largely lost. I have not yet 

 tried the method for transverse sections of the cod's otolith, but doubt 

 if it would be suitable, and in any case the time required makes it useless 

 for practical purposes. 



The following are the details of my observations on specimens of 

 Plaice, Cod, and other species : — 



Young Plaice and Dabs collected by Shrimp-net in Aberdeen 

 Bay in May 1904. 



The plaice in this sample ranged from 5*5 to 8'7cm. in length, 

 and there were very few of them. Unfortunately, they were pre- 

 served in formaline, and when I came to examine them I found that 

 the action of this reagent had altered the otoliths so that the lines of 

 growth could not be distinctly seen. Formaline has a decalcifying 

 action, and although in these specimens the otoliths were not destroyed, 

 they were rendered quite opaque and granular, so that the usual structure 

 was scarcely visible. It seemed probable, however, that they had the 

 characters of the central deposit of the first year, without any sharp 

 dividing lines separating distinct zones. In this case there can be little 

 doubt that the fish were one year old, as the new brood of the current 

 year are still, in May, in the pelagic stage, and it is unlikely that fish so 

 small should be more than one year old. 



The scales are apparently not affected by the formaline as the otoliths 

 are; that is to say the characteristic concentric lines are quite distinct. 

 The posterior or embedded part of the scale consists of five radiating 

 rows of short curved lines, not regularly parallel but irregular, separated 

 by plain bands, while the anterior part of the scale is marked by con- 

 tinuous successive lines approximately parallel to the edge of the scale 

 (fig. 1). There is no division of these series of lines into zones, and 

 the whole may be regarded as the growth of one year. 



Young Plaice from Solway Firth, collected about April 17, 1905. 



The results of examination of the otoliths in these specimens are as 

 follows, males and females being given separately : — 



MALES, IMMATURE. 



(1) 6'Gcm. in length. — Only one central area visible. It contains a 

 central opaque nucleus, the part around which is slightly more opaque 

 than the external zone. Concentric lines of lamination faint (fig. i). 



{2) 6 '9cm. in length. — Only one central area. 



(3) 7'lcm. in length. — Only central area, concentric lines of lamina- 

 tion around the opaque nucleus. 



(4) 7'lcm. in length. — Central area only as in other cases, but near the 

 outer edge a distinct transparent band with an opaque band outside it at 

 the extreme edge. This might possibly be the commencement of the 

 second year's deposit. 



(5) 9 '8cm. — Only one zone. 



(6) 9'9cm. — Two zones. 



(7) 10'5cm. in length. — Two distinct zones, that is to say a distinct 

 zone outside the central area. The central area is *95mm. in the shorter 

 diameter, the total transverse diameter of the otolith being l*92mm. 



