124 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
months, that is, immediately after the minimum of sea tem- 
perature. 
So far as we know each local race, or elementary species 
is characterised by the (approximately) constant habit of 
spawning at the same time of year. Thus we have at least 
two local races in the Irish Sea, the Summer-spawning (Sep- 
tember) Manx herrings, and the Winter-spawning (November- 
December) Welsh fish. The former are fat-rich and the latter 
are (relatively) fat-poor. Further there are morphological 
differences indicated when precise measurements of certain — 
characters are made.* Looking at these differences from the 
point of view of the theory of sampling, the distinction between 
the two races appears very clearly. Both may be regarded as 
belonging to the same population, or local race: if so, the 
differences in value of the diagnostic morphological characters 
ought to be such as to be capable of explanation on the assump- 
tion that they are due to errors of random sampling. Appli- 
cation of the theory of error shows that the probability that 
such is the case is very small and we are forced to conclude 
that the two races are differentiated morphologically as well 
as physiologically. | 
Concomitantly with the metabolic changes in the gonads 
there are changes in the chemical composition of the flesh, or 
rather changes in the ratio of fatty to truly muscular tissue. 
In all races of herrings the maturation of the ovaries and testes 
is accompanied by an increase of fat in the “ flesh,” that is 
by the loading of the subdermal and intermuscular connective 
tissue with fat. For some time before the fish spawns (but 
after the major part of increase in mass of the gonads has taken 
place) the fat-contents decrease, and after spawning this de- 
crease becomes very rapid. Between the time of spawning 
and the time at which maturation of the gonads begins again, 
the fat-contents of the“ flesh” is at its minimum value. This 
* Riddell, Rept. Lancashire Sea-Fish. Laby. for 1915, p. 32. P, the 
probability, varies between <0:000001 and 0°144 for different characters. 
