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they are ordinarily developed while floating, and Hensen has mentioned, 

 loc. eit. pp. 305 — 306 that this it not quite excluded from real life. 



According to Hensen' s investigations there are in the western ijart of 

 the Baltic a great number ot eggs of plaice floating in the water, and he 

 shows that, almost every month there occurs such a low salinity that the 

 eggs must sink to the bottom: and according to his researches they do so at 

 salinities lower than 1, 7S %• 



I have now shown that some eggs can float at salinities as low as 

 l, u °/ , but even such are not always to be found in this part of the Bal- 

 tic. The eggs, consequently, must now and then sink to the bottom in 

 these seas; but whether they are killed by this I cannot tell, though I think 

 it very likely, as they are exposed to many dangers when they touch the 

 bottom; as stated above, however, fry is not found in any great quantities 

 in the Baltic (except perhaps quite exceptionally), at any rate not every year. 



It is not known' if perhaps the young fish which have been hatched 

 from the eggs require a still higher salinity for their further development 

 than the eggs; it cannot be decided, therefore, whether it is this stage which 

 the plaice cannot go through in the Baltic — but nobody, I suppose, will 

 doubt that the hydrographies] conditions excert a great influence upon 

 these matters. — 



It is strange to see the little tender young fish of Pteur. flesiis in 

 multitudes on the shores of the Baltic Sea as far away as Bornhohn, while, 

 so to speak, there is no trace of young plaice. In the salt regions of the 

 (Kattegat on sandy beaches they often live mixed together. Is it now the 

 eggs of Pleur. flesus or the pelagic young ones that can content themselves 

 with a lower salinity than those of the plaice? 



The fry of Rhombus Icevis and particularly of Rhombus maximus are 

 also sometimes met with in multitudes on the shores of the Baltic Sea from 

 which the fry of the plaice is banished. But I am not so astonished at 

 this; for though the eggs of Rhombus maximus*) and lams are evidently 



*) Note: Fertilized eggs of Wiambvs maximus require according to my researches 



a salinity of 2 % in order to float, and will therefore only quite exceptionally he 



able to float in the western part of the Baltic. — 



Cunningham: Studies of the Reproduction and Development of Teleostean Fishes 

 occurring in the neighbourhood of Plymouth. Journal of the Marine 

 Biological Association of the United Kingdom. Vol. I (N. S.) 1889-90, 

 pp. 10 — 54. With 6 plates — gives the specific gravity of the eggs of 

 the following fishes: 



The eggs of Pleuronectes microcephalus floated easily in water of a specific gravity 

 of 1,026, but sank in 1,023; — the specific- gravity of the eggs about 

 1,024. — Corresponds to a salinity of c. 2,9",,— 3%. 



