SEA-FISHERIES LABORATORY. 375 



cient aeration. The eggs develop in these boxes and the 

 larvae after being retained for some time are taken out to 

 sea and " planted " in a suitable locality. It will be 

 obvious from what we have stated above with regard to 

 migrations that the larvae must be set free in such a place 

 that the prevailing winds and tidal drift will carry them 

 to a nursery (which must be present in the area dealt with) 

 in which the conditions for further development are suit- 

 able and in such a time that the assumption of the 

 demersal habit will coincide with the arrival of the larvse 

 on the nursery grounds. The ultimate aim of the hatch- 

 ing operations is to rear the larvae through the period of 

 their metamorphosis under artificial conditions. It has, 

 however, been found extremely difficult to rear even a 

 small proportion through the period referred to since great 

 numbers die during the period immediately following the 

 absorption of the yolk sac. In practice, therefore, the 

 larvae are set free before this mortality has seriously com- 

 menced. The Scottish Fishery Board, in addition to their 

 utilitarian object of adding to the number of young fish 

 in the sea, have since 1897 been devoting attention to the 

 interesting experiment of placing some millions of fry 

 yearly in one limited area where they have reason to think 

 they may be able to test the result by periodic observations 

 on the young fish fauna. In the period between 1894 and 

 1899 inclusive the Board set free 136 millions of arti- 

 ficially hatched larvae, and since 1897 these have been 

 planted in Loch Fyne, the area chosen for experiment. 



The argument for the utility of sea fish hatching 

 rests to some extent on the hypothesis that the period 

 during which the fish are being dealt with in the hatchery 

 is that during which the mortality in nature is greatest. 

 Since, in the hatchery, the eggs and larvae are safe from 

 enemies or prejudicial changes in their physical surround- 



