32 SALMON. 



from what in the Tweed are universally called Smolts, 

 and are acknowledged by all to be the young of the 

 Salmon." 



All these experiments appear to me to be quite con- 

 clusive, and of a nature to satisfy any one who has not 

 pledged himself to an opposite theory. But if any 

 thing were still wanting, it has been completely sup- 

 plied by an additional experiment, which clenches the 

 proof. 



On the 4th of January, 1837, a male Parr, itself the 

 produce of a male Parr and female adult Salmon, was 

 made by expression of the milt to impregnate the eggs 

 of a Salmon weighing twelve pounds ; and for the better 

 security of the lot the whole was placed in a wooden 

 trough, over which a sheet of fine copper wire-gauze 

 was fixed. The trough was then placed in a stream of 

 water previously prepared for its reception, and the 

 results were precisely of a corresponding nature to those 

 already detailed. 



Now, if the Parr and the Salmon were distinct 

 species, their produce would be hybrids, and would not, 

 therefore, breed again, according to the rules of nature 

 established to prevent the confusion of different species 

 by a conservative law ; but this last and most important 

 experiment has proved that the produce from the male 

 Parr and female adult Salmon will breed again with 

 the old Salmon, and therefore that such produce are 

 not mules, but of the same species with their parents. 



In a letter to Mr. Shaw, written in the spring (1840), 

 I suggested to him to impregnate the ova of the Salmon 

 Avith the milt of the common river Trout, imagining 



