238 
Part III. — Tenth Animal licvort 
the species mentioned in the table, and very markedly iu some, instances 
are found in which,' in the same haul of the net, immature individuals are 
captured considerably larger in size than the smallest which is ripe. There 
is evidence, however, in many cases, that this cannot be mere individual 
variation of the kind referred to. A few examples may be given. With the 
common dab, females from 5 to 13 or 14 inches may begot quite immature 
in the same haul with ripe females 6 inches long, e.g., iu one haul on May 27 
of nine females, four, ranging in size from 8 to 14 inches, were fully 
mature, three, from 9 to 12 inches, were approaching maturity, and two 
of 13 and 9 inches were immature; in another haul six ripe specimens 
ranged from 5J to 9 inches, seven, nearly ripe, from 5^ to 7 inches, and 
four, quite immature, also from 5 \ to 7 inches. So with the males ; and 
similar examples might be given among plaice, lemon dabs, witch soles, 
flounder, and long rough dabs. In January, February, and March male 
plaice up to 16 inches long, and females up to 18 inches long, may be 
obtained from within the Forth and in St Andrews Bay, with the repro- 
duction organs quite immature, although the fish are above the size at 
which sexual maturity generally occurs. 
The determination of the size at which maturity is attained does not, of 
course, by itself, throw much light upon the age of the fish. Mr Cunning- 
ham has recently published the results of an investigation on this difficult 
question,* in which the measurements of certain fish confined in tanks, and 
whooe age is known, are compared with those of others taken from the 
sea, the age of which may be in some cases fairly well calculated. 
3. The Duration of Reproductive Life. 
From Table V. it .will be seen that, in almost every case, the ripe, or 
nearly ripe, male is smaller than the female, and that the range of 
difference varies in different species. Further, the maximum size is 
nearly always greater in the case of the female. Another point of 
interest is the difference between the minimum and maximum sizes of 
ripe, or nearly ripe, specimens of either sex, which throws light on the 
duration of the reproductive epoch in the life of the species. Thus, a 
male long rough dab (Hippogloswides Umandoides) may reach sexual 
maturity when only — or even probably under — four inches in length, 
and may continue sexually active until at least twelve inches long. A 
female of the same species may produce ripe ova when about 5 inches 
long, and may go on producing ova, probably once each year, until over 
16 inches in length. A male cod may be ripe when only 18 inches 
long, and live sexually active until it is considerably over 40 inches in 
length. The facts in regard to other species may be gleaned from the 
Table. Unfortunately, we do not yet know very much about the rate of 
growth of fishes ; but, from the observations of Dannevig, Cunningham, 
and others, it would appear that sexual maturity is rarely, if ever, reached 
during the first year of life, and generally not until the second or third 
year, and probably in some cases even later. If this is the case, there 
can be little doubt, from the figures given in the Table, that the duration 
of the reproductive period comprises a considerable number of years 
* Journal Marine Biol. Association, Vol. ii. No. 3, 1892. 
