260 SCIENCE PROGRESS. 



and here comes in one of the features of Dannevig's system. 

 The water which carried the ova to the spawn-collector 

 rushes down an incline to a water-wheel, which moves an 

 eccentric wheel or cam in the hatchino-house. This gives 

 an up-and-down movement to a bar of iron which passes 

 between each series of hatching-boxes (five in number on 

 each side), and has five short transverse pieces, each of 

 which rests on a box. When the rod is raised by the 

 wheel, the buoyancy of the boxes causes them to rise as 

 already mentioned ; but twice every minute the rods fall by 

 the action of a beam on the cam, and each hatching-box is 

 pressed under water by the transverse piece resting on it. 

 Thus, besides the lively current of sea-water constantly 

 flowing in by the broad metal spout at the upper end of the 

 box, the rush of water through the horse-hair cloth on the 

 bottom causes the ova to be in constant movement, and 

 very regularly distributed throughout the box. The sea- 

 water for this purpose is passed through a series of flannel 

 filters arranged on each side (i.e., in duplicate) of the slope 

 between the spawning-pond and the hatching-house, and 

 thus perfect purity is secured. Nowhere could healthier 

 eggs be seen, and when the characteristic yellow pigment 

 appeared in the embryos within them they were even 

 beautiful. At the beginning f the work and when the 

 temperature of the water had an average of 5*24° C, 

 Mr. Dannevig found they hatched in twenty-one days, 

 while towards the end of the operations and when the 

 average temperature was 8*86 ' C, they issued in fourteen 

 days. He kept some in the vessels till the yolk was 

 absorbed and the mouth open, and for a considerable time 

 thereafter, in all for forty-seven days, when an unfortunate 

 accident to the water swept them off. Shortly after hatch- 

 ing (a day or two), the larval plaice turn their heads 

 against the stream and keep in this position, as so fre- 

 quently seen in the case of the young salmon at Stormont- 

 field. The larval fishes, as a rule, are kept in the same 

 compartments until the yolk is nearly absorbed, that is, 

 from ten to fourteen days. They are then conveyed by the 

 steamer Garland to the areas selected in boxes, which are 



