844 PROFESSOR W. C. M'INTOSH AND MR E. E. PRINCE ON 



tion thus produced caused the flounder to dart about with great energy.* Young 

 flounders, colourless, and of glassy transparency, rapidly develop pigment in the laboratory. 



The remarkable appearance of the tail (opisthure, Ryder), with its marginal fringe 

 of rays before any change takes place in the position of the eyes, recalls the condition of 

 the tail in such extinct forms as Kiner's Graphiurus callopterus, in which, however, 

 the vertebral column is prolonged in a straight line, instead of being bent up, and the 

 ordinary caudal rays pass dorsally and ventrally from it. Kiner's form referred to, came 

 from the bituminous shale of Raibl in Karmarthen.t 



The young flounders proceed a considerable distance up the fresh-water stream at a 

 stage somewhat older than the foregoing. 



If the forms observed in the muddy sand of the tidal pools, and also caught in the 

 mid-water net in the bay in April, are the young of the season, their growth is re- 

 markably rapid, even granting a much earlier period for spawning than has been observed 

 at St Andrews (April). 



During April, May, and June, very small specimens of the flounder occur at St 

 Andrews in the shallow rock-pools, containing stunted Algse (Ceramium and other 

 forms), with a slight coating of grey mud. From their translucency the young fishes 

 are invisible, especially on the greyish silt, in which they are often partially immersed, 

 and, as Alex. Agassiz noticed, the two prominent eyes alone attract attention, while the 

 bodies of the fishes themselves cannot be seen. They are elongated and slender, about 

 12 mm. long and 5*5 mm. in total breadth at the widest part. At this stage the true 

 pleuronectid features have been assumed. They swim with the dorso-ventral line horizontal 

 (the right side uppermost), and dart about with rapidity, frequently in confinement leaping 

 over the margin of the vessel. They are fond of attaching themselves to the perpen- 

 dicular sides of a glass vessel, as if their left (white) side had a sucker, but the adhesion 

 is simply due to the muscular action of the whole surface. Both eyes are visible from 

 the right side, though the left eye is more or less lateral in position, or capable of looking 

 slightly downward. In company with them, plaice of the same length occur, being 

 distinguishable as broader and thinner fish, with the left eye not so far to the right, 

 and the ventrals as mere rudiments, while those of the flounder are well formed. 



The flounder is apparently a considerably older fish, and its left side is quite white, 

 while in the plaice the pigments formerly mentioned occur. The coloration of the 

 flounder varies rapidly, and though, when first captured, their anatomy is readily ob- 

 served from their great translucency, yet, as indicated, a few days' exposure to an in- 

 creased amount of light, from absence of shelter in the tanks of the laboratory, causes 

 such a development of pigment, that they are useless as transparent objects. The blackish 

 pigment-spots persisting after preservation, present a close approach to those in the young 

 plaice of the same size. Thus along the dorsal body -line five pigment-spots occur, and 

 four along the ventral line, almost the same number as in the former species. The general 



* The food of these flounders consists of young Gammari and similar Crustaceans, 

 t Sitzungsbr. der K. Akad. Wien. Naturwiss., Bd. 53 and 54, 1866, p. 155, Taf. i. fig. 1. 



