ANNUAL RINGS IN SCALES 489 
Thus the number of sclerites formed seems to follow hand in hand with 
the general metabolism of the animal. 
Little experimental work on the cause of the appearance of winter 
and summer rings has been done. Winge came to the conclusion that 
external conditions were the causative agents, because of the identical 
appearance of the scales of cod captured off the Faroes. 
On August 11th, 1911, six cod were captured and samples of scales 
taken. They were then liberated and were recaptured simultaneously 
nine months later. Of these, three fish of approximately the same size 
were selected, and from each fish five scales were taken, measured and a 
curve made. It was found that all the scale curves thus drawn were 
exceedingly alike, so much so as to include peculiar deviations in the 
course of the curves. Winge argues from this that external conditions 
were responsible for the form of the curves, because the fish must have 
lived together for the nine months before recapture, and must therefore 
have been subjected to similar external conditions, such as temperature 
and salinity. The supply of nourishment in the water must also have 
been the same for the three animals. 
This experiment certainly indicates that it is the environment which 
controls the course of scale growth, but it does not show what particular 
factor is the principal agent. 
J. Stuart Thomson in his paper on the scales of Gadidz (p. 100) states 
that in his opinion it is the amount of food supply, rather than variation 
in temperature, which brings about the formation of annual rings in scales. 
His reasons for coming to this conclusion are two: The first rests upon. 
the evidence afforded by a whiting which was kept in captivity in a tank 
at Plymouth from May, 1902, until July, 1903. The water in the tank 
was not treated in any way, and the animal was fed daily. When in 
July, 1903, the scales were examined the sclerites appeared of the same 
width, and no winter or summer rings were detected. The sclerites also 
seemed to be narrower than is the case with fish captured from the sea. 
This result is in direct opposition to that which I have obtained, for 
my fish in the two tanks when the water was not artificially cooled or 
heated all showed distinct rings. 
Also if food were the determining factor one would have expected that 
a fish fed daily, and which increased in length from 10-20 mm. to 21-5 cm. 
in fourteen months as Thomson records, would have exhibited broader, 
or at any rate as broad, sclerites as fish of the same age captured from 
the sea. Yet this is not so, the sclerites were narrower. 
Again the total number of sclerites produced was about 50, but whiting 
from the sea of the same age showed about 43. This indicates that the 
animal experimented upon was in good condition and corresponded to 
my fish which were abundantly fed. 
