MIDDLETHIRD HATCHING-HOUSE. 117 



which existence is possible are so narrow, without waste there 

 could be no survival. With large numbers the loss of entire broods 

 often opens a more favourable field for the remainder. So with 

 the regulation of water-supply : so long as some waste flows over, 

 so long the pipes and spouts and sluices distribute an even supply, 

 so long, and no longer. It is only to hold as waste, water in 

 excess of the permanent supply, an excess which, if used, would 

 assuredly, sooner or later but most probably very much sooner 

 land the user in trouble, and probably prove the destruction of the 

 whole season's work. Nor should it be supposed this seeming waste 

 cannot be safely utilised. Outside, much assistance can be got from 

 the surplus. The readiest use to put it to is to pass it over the 

 main screen to the works. If this is done with skill, no attendance 

 will be required on that screen a matter of no small importance, 

 as those who have care of fish-works soon discover. The modus 

 operandi will be shown in its place when the intakes come to be 

 described. Enough has now been said to fix the reader's atten- 

 tion on the theory of waste. When his boxes are overcrowded 

 with fry, let him remember the theory of waste, If it is set at 

 nought, disaster will follow. If he is wise, he will pause before 

 he piles his ova inches deep, in the Canadian fashion, as shown at 

 the London Fisheries Exhibition of 1883. 



The first season the incubators in the hatching-house consisted 

 of one set of slate trays and two hatching-boxes of my own design. 

 These were the forerunners of those now so well known at 

 Howietoun ; in fact, they differed only in being half the size. The 

 length was almost the same, but they were only 10 inches wide, 

 inside measurement. As, when I come to the description of the 

 Milnholme hatching-houses, it will be necessary to discuss the 

 general principles governing the hatching of trout ova, it will be 

 sufficient here to consider the mechanical construction of the boxes 

 and grilles. 



The first object is to convey a sufficient supply of oxygen to 

 each ovum ; the second is to arrange so that no sediment may 

 cover the eggs ; the third is simplicity for working ; and the 

 last, protection from injury. The first object is attained by dis- 



