THE FLOUNDER FAMILY. 385 



the young dabs and plaice by the smaller number of fin-rays. 

 Petersen gives in flounders from 8 ram. to 33 mm. long, 49 to 

 65 fin rays in the dorsal fin and 33 to 43 in the anal fin. In 

 addition to this the young flounder is always in a more ad- 

 vanced structural condition than young plaice or dabs of the 

 same size. More pigment is present and the metamorphosis 

 has proceeded further. Later, the appearance of the dorsal 

 and anal rows of tubercles at the base of the fin-rays and at 

 the anterior end of the lateral line at once distinguish the 

 flounder. 



In the month of April, these little fishes may be caught in 

 St Andrews Bay by the mid-water tow-net and many of them 

 present stages in the transformation to the adult one-sidedness ; 

 thus in some the left eye may have only moved a little forward 

 on its own side, in others it may have reached the median ridge 

 on the top of the head, whilst in a third series the eye may 

 have completed its journey and be found on the right side. 

 Together with this movement of the eye, the fish has gradually 

 assumed the habit of moving on its left side, so that at the end 

 of the curious transformation it is admirably adapted for its 

 new habit at the sandy or muddy bottom of the sea-shore. 



A few weeks later the little flounders are to be found along 

 the shore-line, especially at the mouths of streams and rivers, 

 shewing thus early a predilection for fresh or brackish water, 

 which remains throughout life. They are beautifully trans- 

 parent (Plate XVII, fig. 5) and extremely hard to detect when 

 not in motion. In size, they average from a half to two-thirds 

 of an inch in length and when exposed to light in captivity they 

 rapidly lose their transparency by the development of variously 

 tinted pigment of the skin (Plate XVII, figs. 6, 7 and 8). In 

 the grey mud of the rock-pools they disport themselves in 

 company with young plaice of the same size. These are closely 

 similar but, the plaice being a larger fish, a young form of the 

 same size as the young flounder is distinguishable by ' younger ' 

 characters — thus the displacement of the eyes is less complete, 

 the body is broader and thinner and the ventral fins rudi- 

 mentary. We may here quote an observation made some 

 years ago: "The sparrow has been noticed to be destructive 



M. F. 25 



