138 Part II1.—Twenty-third Annual Report 
(2) Length of fish 45°6em. (183 in.), 2} lbs. weight.—Scales behind 
head show two winter zones besides the external edge, in other words 
three annual zones. First zone 12 rings, second 17 to 19, third about 13. 
Otolith also shows three annual zones quite distinctly. Inferred age 
three years. 
(3) Length of fish 67-dem. (2 ft. 3 in.), 8 lbs. wetght.—g with 
small ovary, apparently immature. Scale from pectoral region shows 
three winter zones besides the outer edge, in other words four annual 
zones complete. The first zone contains 14 rings, the second 20, the 
third 16, the last only 7. It might be supposed that the last zone was 
only the commencement of the present season’s growth, or, on the other 
hand, the fourth winter zone might not be complete, as the water is still 
cold in March. I thought it most propable that the fish was four complete 
years old. In the transverse section of the otolith four complete zones 
were visible. In this specimen I examined the pectoral girdle and the 
concave faces of the vertebre. In the coracoid I could with difficulty 
make out three boundary lines in addition to the outer edge, but they 
were very indistinct, and would be untrustworthy without the other 
indications. In the hollows of the vertebra there were numerous con- 
centric lines, -but the boundaries of annual zones were net distinct. 
According to these latter results, the cod at two years of age is 10 to 13 
or 14 inches in length, at three years 17 to 19 inches, at four years 27 
inches ; but of course it would require the examination of a large number 
of specimens to ascertain the average and range of sizes at these ages. 
SPECIMENS oF Cop FROM EXPERIMENTS DESCRIBED BY Dr. FULTON IN 
TWENTY-SECOND Report OF THE Board (For 1903). 
In the last Report Dr. Fulton, in his paper on ‘‘The Rate of Growth 
of Fishes,” described certain experiments on the influence of temperature 
on the growth of cod and other fishes, experiments which were carried 
out in tanks in the Board’s Marine Laboratory at Aberdeen. Several of 
the specimens which formed the subjects of these experiments were sent 
to me by Dr. Fulton, and I have examined them with the following 
results. Some of the specimens were from Tank I., in which the water 
was of the natural temperature, not artificially heated. Dr. Fulton does 
not give any dates in connection with these experiments, but I presume 
that the codling were put into the tank in the autumn of 1903. They 
were then from 12cm. to 15cm. long, or six inches and less. It is not 
certain, but seems most probable, that they were then in their first year. 
They were killed on August 4, 1904, and then sent to me. 
(1) Cod, Tank I., 20-4em. long.—The otolith in transverse section 
shows two annual zones, 7.e. a central opaque region, then a zone of more 
transparent lamin, then a-zone of opaque laminz again. The trans- 
parent zone corresponds to the previous winter, andthe specimen supports 
the view that the opaque lamine are deposited in summer, as they 
extended almost to the edge, showing that they were being formed when 
the fish was killed in August. The specimens were preserved in formaline, 
and the skull bones were rather soft, but the layers of the otolith were 
not obscured. In the scales also a winter zone was visible, the ninth to 
twelfth rings being narrower and closer together. 
(2) 24:8em.—In this also I made out two annual zones in the otolith, 
though the winter zone was not quite so transparent. In the scales the 
winter zone included rings 15 to 21 and was quite distinct, beyond it 
were only seven or eight rings. 
These specimens, therefore, were in their second summer, according to 
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