OF THE SALMONID^. 9 



horizontal section of a wooden tub. The 

 whole apparatus was immersed in water, 

 which was changed every six hours ; but 

 none of the ova reached the tropics alive. 



MR. YOUL'S EXPERIMENTS. 



Eeflecting on this experiment, Mr. Youl 

 set to work in 1854 to study the whole 

 subject of the artificial propagation of 

 salmon and the transport of their ova, and 

 he came to the conclusion that the govern- 

 ing principle must be retardation of the 

 development of the embryos beyond the 

 average natural period, if this could be 

 effected without destroying them. Experi- 

 ments made at the Crystal Palace, in a suit- 

 able breeding-place, had proved that they 

 may hatch at any time between thirty-five 

 days and 140 days from the date of fertilisa- 

 tion, but that the extreme Hmit was most 

 dangerous. This wide range, of course, de- 

 pended upon temperature, and the two ex- 

 tremes represent the highest and lowest 

 temperature that they will endure while pre- 



