34 SALMON FISHING IN THE TWEED 



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 with the milt of the common river 

 trout, imagining that the produce, if any, might 

 be what is called in the Tweed the bull trout, 

 which exactly resembles in outward appearance 

 and general size what one would conceive such a 

 process would create. 



I learn from Mr. Shaw's last paper that he has 

 succeeded in breeding the sea trout by artificial 

 impregnation with their own species ; so that the 

 produce of this cross, that is, of the river trout and 

 salmon, cannot be the sea trout of the Spey and 

 other rivers, but may possibly prove what I sug- 

 gested. It is at least a very curious coincidence, 

 that the Tweed, which abounds in common trout, 

 abounds also in bull trout ; whereas in the Annan 

 and the Tay, where trout are very scarce, the grey 

 or bull trout is very scarce also. But though 

 crosses may be produced by mechanical impregna- 

 tion, it is a matter of grave consideration whether 

 such take place naturally. Trout, however, are 

 always seen near the spawning beds of the other 

 Salmonidce. 



" The young of these sea trout," says Mr. Shaw, 

 "at the age of six months bear no very marked 

 resemblance to the young of the real Salmon, either 



