of the Fishery Board for Scotland. 



239 



Into the top of each transverse partition a short spout of galvanised 

 iron, 3 inches in length, and fths of an inch deep, is fitted (PI. IX., B) ; and 

 in the corresponding edge of the box below another spout, which fits 

 underneath the first, and so directs the water into the box to which it 

 belongs. 



By referring to Plate VIII. the general plan of the hatching apparatus 

 and the course of the water will be easily understood. The apparatus is 

 supplied with water by pipe (E), and as it has a slope from top to bottom of 

 half an inch per foot, the circulation goes on briskly, the water being 

 carried away by the outflow pipe (F). In Plate VIII. a portion of the side 

 has been removed, in order that the mode of circulation in the individual 

 compartments may be the more easily understood. 



The boxes in these compartments, being only attached by one border, 

 float up, and attain their natural level on the entering of the water 

 (PI. VIIL, H). From the spout the water freely circulates around the par- 

 ticular box, passes through its bottom, rises to the surface outside the 

 box, and passes out by a lower spout into the next box. 



If the apparatus is clean, and the water sufficiently salt, it is found 

 that the circulation so caused keeps the eggs floating clear of the bottom, 

 and separate from each other. On the specific gravity being less than 

 that of the eggs, these naturally fall to the bottom, and lodge about 

 the corners. To prevent this, which means failure, a method has been 

 adopted for regulating the current in the following manner : — 



In Plate VIII. will be seen an iron bar running almost the entire length 

 of the apparatus, from K to L. The . end L is fixed, but the lower end K 

 can be moved up and down, and opposite each pair of boxes a short trans- 

 verse bar is fastened (M), sufficient to catch on the edges of the boxes. A 

 cord (P) is attached near the free end of the bar. This cord is in connec- 

 tion with an excentric wheel, driven by an engine, and through the cord 

 the bar is made to rise and fall, through a cleft upright, from four to seven 

 times in the minute. The boxes rise and fall with the bar. The result of 

 this arrangement is that when the boxes are depressed a quantity of water 

 rushes up through the hair net bottom, carrying with it the sunken eggs. 

 The backward current may sometimes be hurtful to the eggs during the 

 early stages of development, but it does not appear to be injurious when 

 the embryo is fairly well developed. The object of this arrangement is 

 to keep the eggs always floating; it is especially necessary when the 

 specific gravity of the water is rather low. Extra outlets are also found 

 to be needed, in the shape of holes below the spouts, in order to relieve 

 the pressure caused in the several compartments by the working of the 

 boxes. 



When the young are ready for hatching the movement of the bar is 

 done away with ; or if in the same apparatus there are other boxes with 

 eggs of an earlier stage still requiring movement, the bar is still allowed 

 to move ; only such transverse pins as are necessary being left. 



If the whole apparatus is working, there will be contained in it about 

 four million eggs. About one half of these, under ordinary circumstances, 

 will hatch out, i.e., two million eggs, or 200,000 for each box. 



In the case of the cod, if the whole apparatus be filled with eggs 

 fertilised at the same time, about two days will elapse between the hatching 

 of the first and the last eggs. The empty egg capsules require to be at once 

 removed; but, as in the cod there are two days between the hatching 

 of the first and last boxes, there is plenty of time for this operation. In 

 the flounder, however, all the boxes hatch about the same time, and there 

 is considerable difficulty in clearing the boxes. When this is not effected, 

 the meshes of the hair net get filled, and the circulation being arrested 



