HATCHING-HOUSES AND APPARATUS; 53 



the pan until the trough is thoroughly cleansed and 

 a little gravel spread over the bottom, when they 

 may be returned to the tray and kept until ready 

 for the pond. If it is intended that the tray be used 

 as a nursery, it should have the orifice of the spout 

 covered with fine wire gauze, to prevent the sud- 

 den disappearance of the fish after the sac has 

 been absorbed, an event of no unlikely occurrence. 

 The windows of the hatching-house should be pro- 

 tected by thick blinds, as the dim, religious light, 

 so often mentioned, is appropriate for the spawn. 

 Direct sunlight is decidedly injurious and fre- 

 quently fatal. We have found a small reflecting 

 lantern convenient in examining spawn. Candles 

 should not be used, as grease falling into the trays 

 may seriously injure their contents. 



The mixed system is a combination of the trough 

 with the grille a slight saving in expense is the 

 only benefit to be derived frgm it, and this is more 

 than counterbalanced by the difficulties met with 

 in their manipulation. If the troughs are long, 

 a slight motion at one end will cause a wave which 

 will be transmitted throughout its entire length, 

 and, as we have found by experiment, seriously 

 disturb the spawn. It will be found to be very 

 difficult to keep the trough clean, and the young, 

 after hatching, fall directly upon the dirt, which 

 has for some time been accumulating, and which 



