DESCRIPTION OF MARINE HATCHERY AT DUNBAR, SCOTLAND. 259 



weighted as just to be sufficiently heavy to depress them. When the rod is raised 

 the buoyancy of the boxes causes them to rise and to regain their former position. 



The movement of the rods is brought about automatically by a system of wires and 

 pulleys, the wires being connected on the one hand with the free end of the rods, and 

 on the other hand with the end of a wooden beam which rests upon an eccentric wheel 

 kept in motion by a waterwheel driven by the overflow water from the spawning 

 pond. As the end of the beam rises and falls on the eccentric the iron rods also rise 

 and fall, and the hatching boxes are raised and depressed. The rise is gradual and 

 the depression rapid, the water in the latter part of the movement being forced 

 upwards through the hair netting and the eggs whirled gently about and kept in con- 

 stant motion. The speed of the eccentric wheel can easily be regulated; about two 

 revolutions in three minutes is generally sufficient. 



The spawning pond or tank, in which the spawning fishes are placed during hatch- 

 ing operations, is constructed of solid concrete sank in the ground, the thickness of 

 the walls at the top varying from 2 to 4 feet. It is 40 feet in length by 11£ feet 

 deep, the breadth at one end being 26 feet and at the other end IS feet, the vari- 

 ation in breadth being due to the nature of the ground. It is capable of containing 

 a little over 00,000 gallons of water. This pond is situated 27 feet from the hatching 

 house, and on higher ground, so that the level of the water in it is about 18 feet 

 above the level of the hatching boxes, and it is inclosed by wooden walls which 

 rest upon the outer edge of the concrete, and is covered by a roofing of galvanized 

 iron with movable skylight windows, which can be darkened when necessary. The 

 upper flat surface of the concrete forms a convenient pathway all round the pond. 



The feed pipe from the pumps is carried along the top and enters at one corner 

 (that furthest from the overflow into the spawn collector), and it is so arranged that 

 the water can be put in at any height. In order to empty the pond, or lower the level 

 of the water, two 4-inch iron pipes pass through the bottom, each controlled by a 

 cock worked from above by a fixed rod, and communicating outside with the waste 

 and drain pipes, and inside with a series of movable perforated pipes lying on the 

 concrete floor, and by means of which the bottom layer of water can be rapidly 

 removed. About 18 inches above the bottom is a flooring of smooth boarding, with 

 spaces between, the width of which may be increased or diminished according to cir- 

 cumstances. The object of this arrangement is to allow excrementitious waters, 

 remains of food, etc., to pass beneath the flooring, whence they may be quickly taken 

 away by the perforated pipes. Three 2^-inch galvanized iron pipes are also carried 

 through the wall at different levels and pass into the filtering gallery; they are 

 provided with cocks, and their use will be presently explained. 



It is into this pond that the spawning fishes, males and females, are placed, and 

 the spawning process, the ejection and impregnation of the eggs, goes on naturally as 

 it would in the sea. As the buoyant eggs rise to the surface they are carried by the 

 overflow into the "spawn-collector.'". The eggs are retained, and the water passes on 

 into the chute to supply the waterwheel for the movement of the boxes, as above 

 described. The spawn-collector consists essentially of a large wooden frame, the 

 bottom, sides, and one end of which are covered with haircloth. It is placed in a large 

 horizontal wooden box, which may be described as a dilatation of the water-chute to 

 the wheel with which it communicates. This box is deeper and wider than the hair- 

 cloth frame, so that a space may exist all around the latter; and it is continuous with 



