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Part III. — Sixteenth Annual Report 



The Fifteenth Annual Report of the Scottish Fishery Board (1897) 

 contains the results of Mr. Dannevig's experiments on the rearing of the 

 young plaice. He gives the measurements of its length and breadth at the 

 various stages, with an account of its food. The life-histories of these 

 forms are described in " British Marine Food-Fishes,"* so far as they are 

 known. Coloured drawings show several stages in the developmenta 

 of each. With regard to the separation of the plaice and the dab Holt's 

 conclusions are accepted. 



The Plaice and the Dab. 



Being, therefore, in the light of recent research, in a more favourable 

 position than Mr. Holt was, these pages contain the results of observa- 

 tions upon the specimens in Professor M'Intosh's collection. 



It was thought that if a series of specimens of each species could be 

 obtained, showing the gradual passing of the larval characteristics into the 

 post-larval, and these into the adult, the separation would be effected. From 

 the collection of Professor M'Intosh, however, half-a-dozen complete series 

 of the plaice and the dab might be obtained with certain portions always 

 the same but other portions different. The variations in the character- 

 istics of these two forms are very great, overlapping at various points 

 during development, so that the notion of a complete series is rather 

 misleading. All that could be done was to separate the portions that 

 were clearly distinct, and then use a calculus of probabilities, as it were, 

 to separate the remainder. 



The flounder is separated from these two forms, chiefly because it 

 undergoes metamorphosis at a smaller size than they do, and because the 

 variations in the number of its fin-rays do not overlap those of the plaice 

 and the dab. 



Eecent research, by Petersen in Denmark, Dunckert at Kiel, Cun- 

 ningham on the east coast of England, and Holt for the west coast of 

 Ireland, has shown that the number of fin-rays of these species is much 

 more variable than was formerly thought, the variations being different in 

 different regions. Yet, as a rule, the flounder is distinguished by its 

 smaller number of fin-rays. The long rough dab and the lemon dab, on 

 the other hand, have a larger number of fin-rays than the plaice and the 

 dab, though the peculiar manner of growth of the fin-rays in the young 

 stages of the long rough dab causes overlapping with the plaice and the 

 dab at these stages. The plaice and the dab, however, overlap at all 

 stages, and this character is not a distinguishing one. After separating 

 the long rough dab, the flounder, and the lemon dab specimens by means 

 of this fin-ray formula, and other characteristics to be mentioned later, a 

 large number of plaice and dab remained. 



These were separated, roughly at first, in various ways. A number of 

 specimens, for example, formed a series from 5 mm. to 12 mm., showing 

 the transition from the earliest, with caudal fin-rays developing, to the 

 latest, with the left eye beginning migration. Such a series occurred in 

 several bottles, and were evidently of the same species — dabs. A number 

 of specimens of the larval plaice, from 6 to 7 mm., and early post-larval at 

 8mm., are present, and these are not to be mistaken for any other form — 

 certainly not the dab. 



* British Marine Food Fishes. M'Intosh and Masterman, 1897. 

 t Var. u. Verwand, r. PL flesus, u. PL flesus. Wissen, Meere, 1896. 



