72 SALMONIA. [SECOND DAY. 



of the egg, which . was still their nourishment. In 

 this state they were easily carried from place to place 

 in confined portions of fresh water for some days, 

 requiring, apparently, no food; but, after about 

 a week, the nourishment in their bag being exhausted, 

 they began to seek their food in the water, and 

 rapidly increased in size. As I have said before, Mr. 

 Jacobi assures us, that the experiment succeeded as 

 well with mature fish, that had been killed for the 

 purpose of procuring the roe and milt, these having 

 been mixed together in cold water immediately after 

 they have been taken out of the body. I have had 

 this experiment tried twice, and with perfect success, 

 and it offers a very good mode of increasing to any 

 extent the quantity of trout in rivers or lakes ; for the 

 young ones are preserved from the attacks of fishes, 

 and other voracious animals or insects, at the time 

 when they are most easily destroyed, and perfectly 

 helpless. The same plan, I have no doubt, would 

 answer equally well with grayling or other varieties of 

 the salmo genus. But in all experiments of this 

 kind, the great principle is, to have a constant current 

 of fresh and aerated water running over the eggs. 

 The uniform supply of air to the embryo in the egg is 

 essential for its life and growth, and such eggs as are 

 not supplied with water saturated with air are unpro- 

 ductive. The experimenter must be guided exactly 



