IIYIJIUDS. 2G7 



eggs were takeu from a Loolilcveu trout and milted fnjiii a "zebra" 8i iiiehcs 

 long. These were ])laced in box '.•2(t. Only about 12 of these eggs eyeil, and 

 merely 3 embryos developed, whilo they died unhatehed. As a rule the eggs 

 appeared not to have been impregnated. On measuring them I found that tlic 

 majority averaged 0*2i of an inch in diameter. The cause of failure in tiiis 

 instance was probably due to the young age of the male. 



Hunter, as we know, was of opinion that hybrids in the higher forms of 

 vertebrates were not i)roductive, except in cases where the genciutive organs were 

 in a condition of perfection, a state which might be considered unnatural in 

 hybrids. But in fishes, the lowest of the vertebrate orders, the labours of fish- 

 culturists lead one to modify those views, while Darwin and others have pointed 

 out that domestication tends to eliminate sterility. It will now be interesting, 

 first, to ascertain the average per-ccntage of salmonoid eggs which are successfully 

 incubated in a well-appointed fish-cultural establishment, and then to compare 

 these with what takes place among hybrids. 



If we place the average proportion of salmon or trout eggs dying during 

 incubation at 5 per cent., such is in reality more than usually occurs atHowietoun, 

 but this figure gives us a basis from which to calculate losses by. But, as I have 

 already obsei'ved (p. 26 ante), eggs from young mothei'S are subject to a greater 

 percentage of deaths during incubation than such as arc (to a certain extent) 

 obtained from fish three or four seasons and upwards of age. While similarly milt 

 from young parents may be a cause of failure in impregnation or mortality among 

 the alevins and springlings. 



In first crosses for forming hybrids, and the first crosses of hybrids, we have 

 the following records : — 



No. of oggs Failures ^°- °^ '^^^'^ 

 incubated. ' mcubating. 



Of course one must not lay too great a stress upon the percentage of losses of 

 eggs during incubation from the number of experiments here recorded, but taking 

 them for what they are worth they would seem to point to the following results. 

 Employing the milt of adult salmon to fertilize trout eggs the loss was as much as 

 28 per cent, and though the mortality among the yearlings and young fish was 

 considerable, such must have been partly owing to the small amount of space 

 which could be accorded to them. 



When we investigate the figures respecting Lochleven trout crossed by salmon 

 smelts or par we find what at first appears strange, that the loss during incubation 

 was far less than when the milt of adult fish was employed. This seems to be 

 pi-obably owing to mechanical causes, as I have already alluded to the size of the 

 micropyle in the trout ova being of barely sufficient extent to admit the spermatozoa 

 of salmon, but owing to the large size of the eggs of these trout at Howietoun this 

 difiiculty has been partially overcome. But employing young male salmon 

 fertilization must be more readily effected, still one point requires elucidation, 



