8 Part I1I.—Twenty-fourth Annual Report 
now somewhat enlarged; a concrete floor replaces the old wooden 
one; a strong wall has been built along the seaward face of the 
site, and granite retaining walls around the gravitation tank. In 
the present Report a brief description is given of the hatchery as 
rearranged, with illustrations showing the interior and exterior, the 
pumping plant, and the large spawning-pond in which the breeding 
fishes are kept and where the eggs are shed at the spawning 
season. 
During last year the eggs of the plaice were first discovered in 
the pond on 20th January, about the usual date when they make 
their appearance. Collections of eggs were thereafter obtained 
almost daily. The numbers gradually increased until the middle 
of March, after which they declined until 16th May, when the last 
collection was made. The duration of the spawning in the pond 
was thus about 117 days, which may be regarded as approximately 
the period in the sea. The aggregate number of eggs collected in 
the season was estimated at 40,110,000, of which 48 per cent. were 
spawned in March, 23 per cent. in February, and the same pro- 
portion in April. 
The duration of the period of embryonic development, until the 
eggs hatch, varies with the temperature of the water. The average 
at the beginning of the season, when the temperature is low, is 
about three weeks; towards the end of the season, with the 
temperature some degrees higher, hatching takes place in about a 
fortnight. The larval fishes, on issuing from the eggs, are retained 
in the apparatus for several days until the yolk-sac is partly 
absorbed, and it is calculated that the eggs and larve are protected 
in this way for about half of the time from the spawning of the 
eggs until the young plaice undergo their metamorphosis and 
assume the form and habit of the adult. 
The estimated number of fry which hatched out and were placed 
in the sea was 24,500,000. Most of them were distributed off 
Aberdeen, but one lot of about three and a half millions was taken to 
St. Combs, further up the coast, at the request of the fishermen, 
and there distributed. 
Since the establishment of the hatchery the total number of the 
fry of plaice which have been set free in the sea amounts to 
387,750,000, the number of fry of other fishes, as turbot, lemon 
dabs, and cod, being close upon 17,000,000. 
Owing to the circumstance that the hatchery is worked in con- 
junction with the Marine Laboratory, the expense of the hatching 
operations is comparatively small, the annual expenditure being 
estimated at rather under than over £100, which meets the cost of 
extra coal and an additional assistant at the height of the season. 
SCIENTIFIC AND TECHNICAL INSTRUCTION TO FISHERMEN. 
For some years past, as mentioned in previous Reports, by an 
arrangement with the Technical Education Committee of the 
County Council of Aberdeenshire, representative fishermen from 
various parts of the coast of that county have visited the laboratory 
and hatchery in spring, to attend demonstrations on the life- 
