50 SALMONID^ OF BRITAIN. 



Changing the conditions of life in an animal, however slight that change may 

 be, might affect the reproductive organs. Thus carnivora, excluding plantigrades, 

 breed freely in confinement ; but carnivorous birds under the same conditions 

 rarely lay fertile eggs; while intercrossing animals of the same species, but 

 belonging to different local races or varieties, generally adds vigour to the mongrel 

 offspring. But if still greater changes are tried, as between two distinct species, 

 a mule or hybrid race is produced which is more or less sterile. The repro- 

 ductive ox'gans in hybrids are supposed to be in an imperfect condition, which 

 would account for such fishes being more difficult to breed from than the pure 

 species. Geoffroy St. Hilaire's experiments proved that unnatural treatment 

 of the embryo occasions monstrosities, while the experiments at Howietoun 

 show that numerous malformations occur when no direct injury or unnatural 

 circumstances (except hybridism, or causes connected with age or consanguinity) 

 could have taken place. Also young parents give weak and often diseased 

 offspring, as well as some monstrosities, which are certainly influences that would 

 affect hybrids as well as pure species. 



Darwin was evidently correct in advancing that the sterility of first crosses 

 with pure species, where the reproductive organs are perfect, depends (often, not 

 always) on the early death of the embryo ; while the sterility of hybrids having 

 imperfect reproductive systems, he considered allied to that sterility of pure 

 species in which the natural conditions of life have been disturbed. But some- 

 thing in addition seems to be necessary in order to account for the monstrosities 

 and diseased forms seen among young hybrid fishes. 



The question arose whether, should an anadromous form of the Salmonidsa be 

 crossed with a non-migratory species, the tendency to migrate to the sea would 

 be lost ? Experiments showed that in such hybrids, until their eggs commenced 

 developing, this migratory habit was in abeyance ; but with the development of 

 the eggs it at once prevailed. 



The question of the prepotency of the sex of either parent in the colour of the 

 offspring, or the period when it breeds, will be deferred until the Howietoun 

 hybrids are considered. 



A thorough investigation into the various forms of Salmonidse present in our 

 waters possesses more than a passing interest ; for if, as some suppose, we have 

 many species of trout and char, and they intercross, it becomes a first consideration 

 as to what are the probabilities of sterility occurring in the hybrid offsprin" ? On 

 the other hand, should trout or char from two (asserted to be) separate species be 

 crossed and no unusual phenomena occur, except improvement in the breed, while 

 sterility is absent and monstrosities or malformations few in number, the 

 supposition must be raised whether we are not dealing with local races instead of 

 with distinct species, and if the young are not in reality mongrels instead of hybrids. 

 Also should hybrid offspring be fertile, it becomes important to ascertain to what 

 extent this fertility extends, and through how many generations it may be found 

 to continue. 



The question of species is also one which greatly concerns the fish-culturist, 

 while systematic zoologists who constitute new forms of trout and char on 

 insufficient grounds, are occasioning great injury to fisheries. For when successful 

 in promulgating their views, they have induced fish preservers to believe that a 

 diminutive race is not the result of poverty of food, or some local cause, which 

 therefore has remained unsought for. While they have also occasioned the 

 eggs or fry of large varieties to be obtained from a distance, often at a great cost, 

 and the deteriorated progeny (due again to the effects of local causes) has been 

 supposed to show that the purchaser had been imposed upon by the vendor thus 

 inducing trouble and needless vexation. 



{Introduction to the Study of Fishes, 1880, page 631) when alluding to the Salmonidie, stated that 

 "some of the species interbreed, and the hybrids mix again with one of the parent species thus 

 producing an offspring more or less similar to the pure breed ;" and a few pages further on he 

 remarked that "the hybrids are sexually as much developed as the pure breed, but nothinc 

 whatever is known of their further propagation and progeny " (I. c. pa-'e 638). 



