SEA-FISHERIES LABORATORY. 129 
possible change ought, however, to be worked out quantitatively 
before it can be regarded as more than possible. 
Temperature alone must be a factor, since during the 
corresponding series of changes in Winter-spawning herrings 
fat accumulates but not to the same extent as in the Summer 
herrings, though the ratio of mass of gonads to total body 
mass is much the same in both categories of fish. In other 
words the temperature function is just that expressed in van ‘t 
Hofi’s law, the rate of chemical change is a function of the 
temperature. There is greater assimilation, and accumulation 
of reserve material, in seasons of high sea-temperature than 
when the latter is relatively low. 
In fact the sexual series of changes can be left out of con- 
sideration in selected cases. Plaice of less than about 30 cms. 
in total length are immature, and the ratio of mass of gonads to 
mass of body does not change throughout the year. But the 
* condition ” of the fish, that is, its weight per unit of length 
varies regularly with the temperature. The expression 
3 
w= kh ue represents this variation in condition with con- 
siderable accuracy, w being the weight of the fish in grammes 
and / its length in centimetres. The coefficient & varies between 
about 0:8 and 1-2, being least at the season of minimal sea- 
temperature and being maximal when the sea-temperature 
is also maximal. A somewhat similar relation holds for the 
herrings investigated here. Weight per unit of length, and sea- 
temperature, are therefore variables which are directly correlated. 
The variation in the coefficient /, in the case of the plaice and 
herrings, means that new tissue is being formed and accumulated 
during the season of rising sea-temperature, and that this tissue 
is being destroyed during the season of falling sea-temperature. 
The tissue that is formed in the plaice seems really to be mus- 
cular substance, but in the herrings it is adipose connective 
tissue. 
