HYBRIDS. 



267 



eggs were taken from a LooHeven trout and milted from a " zebra " 83 inches 

 long. These were placed in box 92a. Only about 12 of these eggs eyed, and 

 merely 3 embryos developed, while they died unhatched. As a rule the eggs 

 appeared not to have been impregnated. Ou measm-ing them I found that the 

 majority averaged 0-24 of an inch iu diameter. The cause of failure in this 

 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 productive, except in cases where the generative 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 percentage of salmonoid eggs which are successfully 

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

 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 reahty more than usually occurs at Howietoun, 

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

 already observed (p. 26 ante), eggs from young mothers are subject to a greater 

 percentage of deaths during incubation than such as are (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 eggs Failures No. of days 

 incubated. ' incubating. 



1881. Dec. 24tli. 

 1884. „ 27th. 

 1884. Nov. 11th. 



1883. „ 2!)th. 



1884. Dec. 'Ml. 



1883. Nov. 29th. 



1882. „ 15th. 



1883. „ 29th. 

 1882. „ 15th. 



1885. Dec. 5th. 

 1882. Nov. 15th. 



1884. „ 12th. 



1885. „ 25th. 



1884. Deo. 6th. 



1884. Nov. 12th. 



1885. Dec. 5th. 



1886. „ 5th. 

 1884. Nov. 12th. 



Male salmon (adult) and Lochleven trout 



( „ ) ., 

 (young) ,, 



( „ ) „ 

 Male Lochleven trout and salmon (young) 

 Male sahnon (young) and American char 

 Male American char and Lochleven trout 



n n M n ,1 



Male Lochleven and American char 

 Male British char and Lochleven trout 

 Male American char and British char 

 Male struan (young) and struan 



zebr 



bra ( 



Lochleven 



British char 

 Lochleven 



20,000 



7000 



12,000 



4500 



400 

 3695 

 3000 

 3000 

 8000 

 6500 

 9000 



146 

 12,000 



600 

 4500 

 7000 

 1200 

 1350 



about 28 per cent. 



„ 19 

 



„ 62 



„ 93 



„ 17 



„ 15 



„ 32 



„ 99 



„ 23 



„ 99 



„ 83 



„ 91 



„ 63 



„ 78 



„ 99 



„ 100 



75 

 76 

 78 

 78 

 78 

 83 

 85 



84 

 84 

 86 

 83 



79 



77 

 77 



Of course one must not lay too great a stress upon the pei-centage 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 figux'es respecting Lochleven trout crossed by salmon 

 smolts 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 

 probably 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 

 difficulty has been partially overcome. But employing young- male salmon 

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



