1896] Summary. 19 



salt water (3 — 4 %o), the roe remained rather softer than after 

 fresh water fertilization. 



The cause, in my opinion, is of a physical nature. The cir- 

 cumstance that the roe fertilized in salt water remained so long 

 soft, arises from the fact that sea-water is less easily diffused 

 through the egg membrane than pure fresh water; for it has been 

 demonstrated that salt solutions are diffused more slowly through 

 membran es than fresh water. 



I will not here express any decided opinion as to how far the 

 fecundation of salmon spawn can take place in water containing 

 about 30 %o salt. The question will be tåken up ; for renewed 

 investigation in the autumn. In the mean time it is certain that 

 of a quantity of fertilized salmon spawn placed in sea-watei J on the 

 Ist Nov. 1895, the whole became by degrees shining and trans- 

 parent, with a reddish yellow circular spot on one side. In order 

 to test the vitality of the spawn, some of it was placed in fresh 

 water. All the eggs then very soon turned white, or, in other 

 words, assumed the appearance which dead salmon spawn presents 

 in fresh water. By once more transferring the roe to sea-water, it 

 reassumed its former transparency and shining appearance. I have 

 repeated this experiment innumerable times, alvvays with the same 

 result. The above-mentioned change has also been observed by 

 other investigators, and among them by mr. Simonnæs, Fisheries assi- 

 stant. Notwithstanding repeated attempts, we were not successful 

 in hatching salmon spawn in sea water, even when the spawn had 

 been fertilized in fresh water. . 



The sea-trout from which the spawn was tåken had been 

 caught in salt water, and had lived in salt water until it arrived 

 at sexual maturity; and on the 6th Nov. we obtained some ripe 

 spawn, of which 175 cubic centimetres were fertilized in salt water, and 

 placed in sea-water. On the llth of the same month, all the eggs were 

 transparent, with a reddish yellow spot, like the salmon spawn 

 under similar circumstances. In order to test whether sea water 

 had a deleterious effect on normal, fertilized salmon spawn 

 which had lain for some time in fresh water, 100 pieces of roe 

 thaf had been in fresh water for 4 days were placed in sea-water. 

 At the end of 3 days, 63 of them were dead, and 3 days later, all were 

 dead. The test of the actual destruction of the vital germ in this and the 

 other cases, was found by placing the eggs in fresh water, where 

 they turned white. If, on the other hand, the spawn was trans- 



