[13] EGGS OF THE PLAICE, FLOUNDER, AND COD. 439 



not be taken into account, because in natural impregnation the spawn 

 immediately become mixed with the overplus of the surrounding me- 

 dium. 



I have also made experiments with solutions of rock-salt and of sea- 

 salt which was not quite dry. The results were the same, and I found 

 it impossible to dilute the solution of rock-salt as much as that of sea- 

 water, without decreasing the mobility of the spermatozoa. The spawn 

 of the plaice acts the same way as that of the cod. 



This experience cannot, in my opinion, be generally applied, for 

 otherwise the propagation of fish in the eastern part of the Baltic would 

 come to a standstill, whilst we know that both cod and flounders are 

 found beyond Memel. I am not able to furnish an explanation of the 

 matter. In order to do this direct investigations would have to be 

 made ou the spot. 



For the questions which both here and later will be of interest, the 

 composition of the sea- water is of greater importance, as for instance, 

 it cannot be immaterial what kind of salt is dissolved in the spawn 

 mixture. I, therefore, give below the latest results as to the composi- 

 tion of the sea- water, from the analyses of the Norwegian expedition, 

 principally based on Schmelck's * analysis, arranged in tabular manner 

 for immediate practical use. 



According to Jacobsen t the calcium in the Baltic amounts to 1.208 

 and 1.337 per cent. He also finds that the average quantity of sul- 

 phuric acid in the ocean is 6.493 per cent, of the salt a difference which 

 would not be equalized, even if the salt was calculated at 99.6, instead of 

 100 parts. The remaining 0.36 parts are probably composed of iodine 

 and bromine. 



But to return to the eggs. It has already been shown that the eggs 

 can develop both when floating near the surface and when lying at the 

 bottom. The danger of their being devoured, therefore, seems to be 

 varying according to circumstances. The floating eggs may be carried 

 ashore, which, however, occurs comparatively seldom, or they may be 

 devoured by other marine animals floating about near the surface. I 

 do not consider these dangers as very great, but will, nevertheless, 

 report on this subject below. In my opinion the danger is much greater 

 when the eggs lie on the bottom. Here crabs, snails, worms, and star- 

 fish are crawling about in large numbers; here shell-fish of different 

 kinds, hidden in the bottom, whirl the currents of water which contain 

 their food into their interior. Every fish floating past moves the water 

 sufficiently to drive the eggs along the bottom and bring them within 

 the reach of these whirlpools. In fact, the possibility of being devoured 

 seems much greater. I am, so far at least, not able to form a definite 

 opinion as to the quantity of marine animals at the bottom of the sea, 

 which probably varies greatly in different locations. By digging in 



* Schmelek: " Der Norske Nordhaoa expedition." Christiania; 1882. 

 i Jahreahericht, 1871, p. 55, and 1874-76, p. 241. 



