482 D. W. CUTLER. 
Before putting the fish into the tanks scales were taken from the 
regions just above the pectoral fin and examined and scale curves 
made from each specimen. 
The length of each fish was recorded and the animal marked. This 
was done by tying pieces of various coloured silks round the tail. 
The experiments started about the middle of July, 1915. On January 
9th, 1916, each fish was re-examined and scales taken from the same 
region as before, the length also being recorded. 
The fish were then allowed to remain undisturbed until the following 
May, when about half a dozen from each tank were killed by chloroform, 
and scales again taken. This method of procedure was necessary because 
of my having, during the course of the experiments, removed from 
Plymouth to Manchester and I was unable to go to Plymouth in order 
to remove the scales from the living animals. The remaining fish were 
kept under experimental condition until the beginning of October, 1916, 
when they were killed, measured, and scale samples sent to me. 
The experimental conditions under which the animals lived were as 
follows: the temperature of the water in two of the four tanks was 
varied, one being kept at a temperature as high or higher than the 
normal summer temperature of the sea water in the tanks at 
Plymouth, while the temperature of the other was kept as low as 
possible. 
The remaining two tanks were used for feeding experiments, the 
temperature being that of the sea water in circulation in the tanks 
at Plymouth. 
HOT AND COLD TANKS. 
The temperature in the hot tank was obtained by running in sea water 
that had previously been heated. During the first part of the experiment, 
that is from July to January, the results were not very satisfactory, 
because the heating apparatus was turned off during the night and the 
tank water allowed to cool. Although it never reached the normal 
temperature yet there was a difference of 3-4° C. between the night and 
day temperatures. After January, however, a new apparatus was kindly 
devised by Mr. Matthews which maintained the water at a constant 
temperature day and night. 
The artificial cooling of the cold tank was done by running sea water 
through glass tubes, which were surrounded by ice. This apparatus was 
quite successful in cooling the water, but as the ice was not renewed 
during the night the temperature of the tank rose a little. The result 
of this was a shghtly fluctuating temperature, which was, however, not 
sufficient to nullify the experiments, the fluctuations not being more 
than 3° C. in the summer, and between 1° and 2° for the winter and 
autumn. 
