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It seems as if turbots, compared to brills of the same length, are somewhat 

 jn advance in their development. When 7 — 8 mm , for instance, the turbot has 

 traces of true rays in all the median fins, and chorda is curved considerably up- 

 ward in the tail; brills of this length have scarcely any but embryonic rays in 

 all the fins (though the fins are all formed) and chorda is curved only a little 

 upward. — The turbot is often more pigmented on the body than the brill. 



In young turbots of 10 — 11mm (plate I, fig. 3 & 7), the spiny equipment 

 of the head is fast developing while in brills of the same size we can discover 

 only slight traces of it by means of the microscope. The turbots are always in 

 advance of the brills in development, and more pigmented on the body. In all 

 median fins true fin-rays are formed, though not in the full number ; we may see 

 however, whether we have before us a form with many rays (brill) or with but a 

 few ones (turbot), as there are only wanting a smaller number at the ends of the 

 median fins. Both species are at this stage very longish. 



This stage forms the transition to the above-mentioned (not represented) 

 young ones of c. 15 mnl , which again by little and little enter into the following 

 stage, the young fish of c. 20 — 22 mm (plate 1, fig. 2 & 6); nay, the transition is 

 so even that we can scarcely speak of different stages. It is not till the fish from 

 their pelagic life enter into the life on the bottom that we can indeed speak of 

 a new stage: the bottom stage. 



At the bottom stage (plate I, fig. 1 & 5) all the spiny adornments of the head 

 have disappeared, with the exception, perhaps, of a slight trace of the crest on 

 the left side of the turbot, now situated between the eyes. Both eyes are situated 

 on the left side, which is highly pigmented, while the right side is without any 

 pigment. All fins appear to have their full number of rays, and the form of the 

 fish is in the main like that of the grown-up one. — The pigmenting is to a cer- 

 tain degree characteristic of either species, but it is a difficult thing to express 

 the difference in words. When I say that the body of the turbot has often large 

 pale spots, while other parts of the body and the fins are dark, and that it has 

 often light spots on dark ground, while the colours of the brill are more dotted 

 about, this is but in part an appropriate description. 



I have turbots, only 18 mm long, which are fully metamorphosed, while the 

 above-mentioned turbot, which was not yet quite metamorphosed, was 22 mm . 

 Can this be owing to an individual variation, or do the animals become shorter 

 by the metamorphose? Something like this seems to take place also in the brill 

 and the plaice*). 



Also the transition of the plaice from the pelagic stage to the bottom stage is ac- 

 companied "by a thorough change in many of the organs of the flat-fishes. The 

 skin of these fishes seems to change, also the muscles, I dare say. The whole bulk 

 of the fish is smaller, and after the metamorphose it is thinner than it was before, 

 particularly in the fins. The specific gravity of the fish is evidently much higher. 

 This will apply to the young ones of all the flat-fishes I have studied. 



