368 
plicable on the principle which occasions the large growth of 
the capon” (Charlesworth, Mag. Nat. Hist., 1837,1., p.84). Here 
hybrid males are considered incompetent to fecundate, and if 
we refer to Professor Kuhn’s experiments, we also find it recorded 
that the gayal and Huropean domestic ox had commingled and 
many hybrids resulted; that of these hybrids the females paired 
with European bulls of unmixed blood, but that the hybrid bulls, 
without exception, proved absolutely sterile, although they 
readily paired with hybrid cows of unmixed European races. 
But we do not find this to be the case in fishes, where 
male and female hybrids (American x British char) have freely 
interbred, and even the males of these hybrid races have inter- 
crossed with pure Lochleven trout; while I have already 
alluded to the mechanical difficulty in breeding from very young 
fish, which sometimes results in non-impregnation, high mor- 
tality during incubation, deformities of offspring, or very 
many losses among the young, apparently from deficiency of 
vitality. 
- The degree of fertility in hybrids has been said to be in the 
ratio of the affinity between the parents; and that all true 
hybrids that have been productive have been raised from species 
brought from remote countries, and more or less in a state of 
domestication. 
The Howietoun crosses give the following results :— 
4-year-old Lochleven trout x salmon milt gave a fertile hybrid, a 
male of which was used with success to cross a Lochleven trout. 
8-year-old Lochleven trout x salmon par milt gave a fertile hybrid ; a 
female of this was crossed with success by a Lochleven trout. 
Female American char X salmon par proved fertile. 
u u »  Lochleven trout proved fertile. 
Lochleven trout X Windermere char proved fertile. 
» American char X Scotch char proved fertile, and the hybrids 
formed a fertile cross among themselves ; also with the Lochleven trout, and 
this second generation of hybrids also proved fertile. 
But although the foregoing demonstrates how various species 
of salmonide may hybridize and interbreed, it becomes necessary 
