46 PACKING THE TROUT OVA. 



thrown on to the frames until one-third of the period of incuba- 

 tion has elapsed. If removed from the hatching-boxes before the 

 formation of red blood, the loss in packing would be very great, 

 generally sufficient to cause the loss of the whole consignment. 

 Eggs, of course, can be packed with safety immediately after 

 impregnation ; but after the germ rises and segmentation com- 

 mences they become more and more delicate, until about 17 per 

 cent, of the period of incubation has been accomplished, when a 

 very slight disturbance will cause death. After 25 per cent, of 

 the period of incubation has been accomplished the ovum can be 

 handled safely only when great care is exercised ; but after 30 

 per cent, has been completed the embryo no longer resents hand- 

 ling, in fact, at this stage, the ovum can frequently be dropped on 

 to a wooden table from a height of 12 or 14 inches without 

 sustaining any apparent injury. This, therefore, is a most favour- 

 able stage at which to pack ova for long voyages, especially as 

 the remaining two-thirds of the period of incubation can be 

 spread over sixty days without much injury to the future fry. 



TEMPERATURE TO BE MAINTAINED DURING TRANSPORTATION. 



In ordinary cases, where the ova is packed on damp swan's 

 down between pads of tolerably dry moss, no precautions as to 

 temperature are necessary, beyond a little care in filling the saw- 

 dust equally round the interior box ; but if the ova are on the 

 point of hatching, and the length of journey uncertain as in the 

 case of Ireland, and many parts of the Scotch Highlands judg 

 ment must be exercised to determine whether the eggs should 

 be retarded by means of ice filled into the air-tray. At a low 

 temperature ova require very little air, but plenty of moisture ; 

 but in a temperature between 40 and 50 the ova require plenty 

 of air and very little moisture. So long as the eggs are sufficiently 

 backward to enable them to be packed in the dry method, the 

 matter is very simple ; but it is often necessary to stock redds in 

 almost inaccessible positions, and, where it is highly important, the 

 alevins are hatched immediately the eggs are laid in the redd. 

 Pounded ice must be filled into the air-tray, and as it melts the 



