120 SEASON 1874 75. 



and although the embryos are still alive, the smell in the room will 

 be overpowering. A small room is the best for this experiment ; 

 if the temperature is above 50 F. one night is sufficient. 



Another mode of demonstrating the exudance of gases by the 

 ova is to place a single ovum on a plate of glass, or between two 

 glass rods, with only a drop of water, and in a damp atmosphere ; 

 and also lay a few eggs on damp live moss, and some on swan's 

 down in the same atmosphere. In a couple of days the embryos in 

 the ova in the drops of water on the glass will be dead, with the 

 white streak so suggestive of suffocation ; those on the moss will 

 be as fresh as the moment they were laid out, and those on the 

 swan's down pale, but quite alive. This shows the first were 

 suffocated by the deficiency of oxygen, caused by the gas given off 

 by the ovum being retained by the drop of water, and possibly 

 forming a cloud round the ovum, as at first sight one would sup- 

 pose that in air (which surrounds the top half of the egg, for the 

 drop need not cover the ovum to drown it) oxygen would have 

 free access and preserve life ; but it is not so. Those on the moss 

 do best, because the live moss feeds on or rather absorbs the gas 

 given off by the embryos, leaving the shell free to receive all the 

 oxygen necessary for the growth of the future fish. In the last 

 case, the swan's down acts merely by capillary attraction, and the 

 result is a pale embryo, the gases having only been partially 

 removed, and still to some extent preventing the free absorption 

 of oxygen. In the above experiments the temperature never fell 

 below 45 or rose above 50 F. In a low temperature the life 

 of the embryo is so sluggish that no difference would have been 

 perceptible between the three lots in two days. Had the tem- 

 perature been high, and the eggs nearly hatched, those on the 

 moss would still have received no injury, as the moss would itself 

 have stimulated into quicker action, unless, indeed, some of the 

 alevins were hatched prematurely ; those on the swan's down would 

 become very pale indeed ; and those in the drops of water would 

 die in less than twelve hours. These experiments are of the 

 utmost importance in connection with the transportation of salmon 

 and trout ova. 



