ARTIFICIAL HATCHING OF SPAWN. 53 



properly fecundated by the milt of the male. Indeed, 

 if the eggs get over from forty-five to fifty-five days 

 without showing the eyes, there is little or no hope 

 of them. Large numbers of eggs will often go bad 

 about the same time, or at various periods, without 

 any apparent cause ; and when this is the case the pro- 

 bability is that they have been taken from an unripe 

 fish, or one not in fit spawning condition. These also 

 retain their appearance for a time, but go off at last. 



Ova of salmon, it has been been generally supposed, 

 require from 70 to 120 or 130 days to hatch ; but 

 this would, probably, be under water at very low 

 temperatures, possibly from little above freezing to 

 36° or 38°, for a longer or shorter portion of that 

 time, and thus the hatching would be much retarded. 

 When placed in water of a higher temperature, how- 

 ever, ranging from 40° to 50°, this period is very 

 sensibly abridged ; and ova hatched in the greenhouse 

 apparatus, as far as we could ascertain, did not exceed 

 from sixty to seventy days — a material difference ; 

 and in this apparatus the water ranged from about 

 42° to 48°. 



The bulk of the trout ova, however; hatched in from 

 fifty to sixty days. They were afterwards conveyed 

 down to the meadows, and placed in a spare box 

 there, as the waters in the greenhouse troughs became 



