480 D. W. CUTLER. 
for its age, while the second one, of length 44:4 cm. was about normal, 
thus it seems to me as though the first fish instead of showing an inten- 
sive growth rather exhibited a slow one. If this is so the conclusion 
Thomson arrived at is practically reversed, and rather is in accordance 
with my results. 
Cases are often seen where a fish is in good condition, but the total 
number of sclerites is somewhat small as is also the length ; such a one is 
the 43 year old fish of length 27°8 cm., the scale curve of which is seen in 
Fig. 4 A. The condition when examined was excellent, and one would 
have thought the length would have been greater. The number of 
sclerites formed during each year of growth is, however, instructive ; 
during the first year there were nine, the second eleven, but during the 
two following years this number was increased to twenty-four for the 
third and twenty for the fourth year. I should interpret this as meaning 
that during the first two years of lite the conditions for growth were 
unfavourable, but that they improved later on. This is borne out by 
the four-year-old fish, of length 26°38 cm., whose scale curve is seen in 
Fig. 4 X. The condition of the animal was poor when examined and the 
total number of sclerites very few, thirty-four. During the first year 
only four were produced, and but six and five for the third and fourth 
years respectively. The number sixteen for the second year seems to 
indicate a period of more favourable conditions. 
A summary of the first part of my investigations is that the age of 
Plaice and probably Flounders can be accurately ascertained by the 
examination of the scales without reference to the otoliths. Having 
seen that two distinct breadths of sclerites are produced during each 
year, the problem arises as to what are the factors concerned in their 
production, and it is with the experiments which I performed in order 
to ascertain this, that the next part of the paper deals. 
PART II. 
Previous workers on fish scales have assumed that the annual rings 
are produced either by seasonal variations in the temperature of the 
water, or by fluctuations in the food supply. I therefore resolved to 
ascertain by experiment what part these two factors actually played in 
scale growth. 
METHODS. 
Four tanks at the Plymouth Laboratory were placed at my disposal 
and into each of these from 12-16 fish were placed ; both Plaice and 
Flounders being used. 
