of the Fishery Board for Scotland. 



139 



the structural indications, and this conclusion seems to be in accordance 

 with the actual age. 



Whiting from Tank I., c 2J/.'8cm. long.— Otolith shows one complete 

 year and commencement of second, i.e. dark central region, then trans- 

 parent zone, then dark external zone. The scales also show a distinct 

 winter zone ; there are 14 summer lines, then 12 winter lines, ending in a 

 very distinct boundary of one or two very narrow rings ; outside this 

 boundary the new summer growth shows only seven or eight rings. 

 Evidently the growth of the year is not very large even at the beginning 

 of August. These whiting were 14cm. to 20cm. long when put into the 

 tank, and it might be thought that they must then have been in their 

 second year, but the structural indications are that the fish were only in 

 their second year when killed. 



Cod from Tank No. length, S6'6cm. ; hilled November 5. 1904. — 

 I only received one specimen from this tank, which was kept artificially 

 warm during the winter 1903-04. This, however, had not prevented the 

 appearance of the boundaries between the annual zones of growth, for the 

 transverse slice of the otolith distinctly shuwed two annual zones, and 

 showed also a transparent zone externally in addition to the layers seen in 

 the specimen killed in August. The scales also showed one winter zone 

 at rings 15 to 20, and outside this 19 rings. To anyone who refers to 

 Dr. Fulton's paper this will not seem surprising, for his tables show 

 that, in spite of the artificial increase of temperature in the tank 

 in winter, the cod grew nearly twice as fast in the last 55 days of the 

 experiment than in the first 100. The growth was therefore slower in 

 the winter, and the reduction of growth is shown by the winter zone in 

 otolith and scales. 



LITERATURE. 



Thomson, J. Stuart — "Periodic Growth of Scales in Gadidse as an Index of 



Age." Jour. Mar. Biol. As*., Vol. xii., No. 1, 1904. 

 Reibisch, Johannes — "Ueber die Eizahl bei Pleuronectes platessa und die 



Altersbestimmung dieser Form aus den O tori then." Wissenschajtliche Uvfer- 



suchungen Komm. deutsch. Meere, Bd. iv. , Abt. Kiel, 1900. 

 Jenkins, J. T. — "Altersbestimmung durch Otolithen bei Clupeiden." Ibid, Bd. 



vi., Abt. Kiel, 1902. 



Fulton, T. W. — "The Rate of Growth of Fishes." Twenty -second Annual 

 Report, Fishery Board for Scotland, Part III., 1904. 



DESCRIPTION OF PLATES. 



PLATE VII. 



Fig. 1. Scale ot Plaice, 8 "7cm. long, caught near Aberdeen, May 1904. Zeiss 

 a 2 Oc.3 camera. 



Fig. 2. Otolith of Plaice, 5 - 6cm. long, hatched in the spring of 1903, reared in 



small tank, and killed Nov. 5, 1904. Zeiss a 2 Oc.2. 

 Fig. 3. Scale of same specimen, actual length •29mm. Zeiss A Oc.3. 

 Fig. 4. Otolith of Plaice, 6*6cm. long, d>, from Sol way Firth, caught April 1905. 

 Fig. 5. Otolith of Plaice, 37*5cm. (15 inches) long. Zeiss a 2 Oc.2. Shows 



seven zones, indicating apparently seven years of age. 

 Fig. 6. Otolith of Plaice, 12*2cm. long, from Solway Firth, caught April 1905. 



Zeiss a 3 Oc.2 camera. Shows two annual zones. 

 Fig. 7. Otolith of Plaice, 22*9cm. long, caught near Aberdeen, April 1, 1905. 



Zeiss a 2 Oc.2 camera. 

 Fig. 8. Otolith of Plaice, 9'2cm. long, $ immature, from Solway Firth, April 



1905. Zeiss a 3 Oc.2 camera- 



