OF THE GRIMSBY T'RAWL FISHERY. 374 
seems to me to be explicable by a condition peculiar, so far as I 
know, to fishes. We have abundant evidence, thanks to Cun- 
ningham’s researches, of the great variability of the rate of growth 
in Teleostean fishes, but all our studies of the life-history of the fish, 
especially of those forms which show a marked difference of dis- 
tribution at different stages of growth, seem to show that it is size 
alone and not age which is the determining factor in distribution. 
That this should be so is not remarkable, if we accept the hypothesis 
that it is the quest of suitable food which induces the changes, since 
a dwarfed individual, however old, would not be likely to require 
more or different food than its younger but more rapidly developed 
brethren. I believe there is the same relation between size and 
sexual maturity to this extent,—that a fish which reaches a certain 
(approximate) size at the season when the roe or milt commences to 
ripen, develops in due course into a spawning fish at the next spawn- 
ing season. But if the fish is a little short of the required standard, 
its maturation is delayed for another year. During this period its 
growth does not cease, but is probably all the more rapid because 
there is no drain on its resources from the generative organs, and so 
the fish, before it spawns for the first time, has reached a size con- 
siderably greater than that of the smallest spawning fish of the 
species. Probably, in some individuals growth is so retarded that 
even a moderately large size is never reached, and yet we do not 
find very small ripe fish (at any rate among the female sex), and I 
do not see how this can be explained except on some such hypothesis 
as I have put forward. 
In considering the method of distinguishing sexually mature and 
immature fish at a period remote from the spawning season, or in 
cases where the roe is only slightly developed, we must consider the 
changes that this organ goes through in becoming mature. In the 
immature female the ovary, so soon as it is large enough to be easily 
perceptible, is found to contain a number of minute translucent ova, 
their size and condition depending neither on the season of the year 
nor upon the size of the fish. ‘he first approach to maturity is 
denoted by an enlargement of some of the ova, and by various 
changes in their internal structure. The most noticeable of these 
changes is the formation of yolk matter, since, as has been shown by 
Mr. Cunningham,* it is that which gives to the ova an opaque 
appearance which they do not previously possess, and for purposes 
of convenience I have called the minute translucent ova “‘ inactive,”’ 
applying the term ‘active ”’ to those which have become opaque. 
* Mr. Cunningham’s paper (‘ Journ. Marine Biol. Assoc.,’ N.S., iii, p. 154) deserves the 
closest attention in this connection, the more so since, as will appear later, his views differ 
slightly from my own. 
