14 Part ITT —Twenty-fourth Annual Report 
trawlers employed in the trawling investigations, as previously 
described, and is the same method as that which has since been 
used so extensively in the course of the international investigations 
in the North Sea. During the course of the investigation, which 
has extended over six years, the numbers of the chief species dealt 
with have been as follows :— 
Plaice, . : a UAL) Whiting, ‘ ~ 583164! 
Common Dab, a 262230 Gurnard, : 5,495 
Long Rough Dab, . — 20,261 Norway Pout, : 7,192 
Cod, i : ; 7,176 Herring, 5 . 19,806 
Haddock, : . 28,760 Sprat, 6,473 
From a study of the growth of the different fishes and the size 
at which they attain maturity, a law of growth is stated, namely, 
that fishes approximately double their size and increase their 
weight about eight times after they have reached sexual maturity. 
The species whose growth and age are specially dealt with in 
the paper are the plaice, dab, flounder, lemon dab, long rough dab, 
turbot, brill, cod, haddock, whiting, and grey gurnard. A general 
conclusion is that fishes do not grow so quickly as is generally 
supposed. Thus, while the plaice reaches a length of about three 
inches in the first year of its life, the female is five years old and 
the male four years when they attain maturity. It is estimated 
that the turbot does not spawn until it is at least seven years old, 
while the cod spawns at four or five years, the haddock at three, 
and the whiting when two years of age. The paper is accompanied 
by a number of tables of measurements and two plates. 
In connection with the question of the growth of fishes, a research 
on the rate of digestion by Dr. Noél Paton, whose investigations on 
the salmon are so well known, is in progress. Two sets of observa- 
tions have been made, but the final results are reserved for next 
year’s Report. 
Tue Tay SPRAT FISHERY. 
Mr. John Fletcher contributes a paper on the sprat fishery in 
the Tay, similar to the one published last year, but dealing with 
the winter of 1905-1906. The fishery was again a comparative 
failure, only 1371 crans of sprats, including young herrings, being 
taken. The estimated number of young herrings caught in the 
sprat fishing is stated to have been nearly 12,000,000, while the 
sprats are estimated at a little over 16,000,000, the estimated 
percentage of young herrings amounting to 42:4. 
THE SPECIFIC CHARACTERS OF THE GADIDZ. 
Dr. Williamson contributes a paper, illustrated with three plates, 
on the classification of certain members of the cod-family, viz., the 
bib, or whiting-pout, the poor-cod, and the Norway pout, the paper 
being a continuation of a previous one, in which the cod, the 
saithe, and the lythe were dealt with. Two of the species, the 
whiting-pout and the poor-cod, have often been confused, certain 
