THE FLOUNDER 255 



form of spinous tubercles are also present, usually- 

 forming a group near the origin of the lateral line 

 and a series along the bases of the dorsal and anal 

 fins, corresponding to the interspaces between the 

 rays ; the lateral line is nearly straight, with a slight 

 curve above the pectoral fin. 



Like most Flat-fishes the Flounder is able to 

 change its colour according to the nature of the 

 ground, and the resemblance to the sand, gravel, or 

 mud on which it lies is so perfect that it is almost 

 impossible to see the fish unless it moves. In this 

 species it has been definitely established that the 

 contractions and expansions of the pigment cells 

 are under the control of the nervous system, and 

 that the perception by the eye of the colour of the 

 bottom is necessary for the assumption of a similar 

 appearance by the fish. 



The colour is often greyish olive, occasionally 

 marbled with brownish ; but it varies from nearly 

 yellow to almost black ; orange spots like those of 

 the Plaice are sometimes present. The latter fish 

 is the nearest ally of the Flounder, from which it 

 is especially distinguished by the more numerous 

 dorsal and anal rays, the shorter caudal peduncle, 

 the absence of spinous tubercles on the body, and 

 the presence of bony knobs on the postorbital ridge. 



Reversed examples of the Flounder, i.e. specimens 

 with the eyes and colour on the left side, are fairly 

 common, and in some localities are at times as 

 numerous as the others. 



Ambicolorate Flounders are by no means rare, 

 and it is interesting to note that many of these are 

 not only symmetrical in having both sides coloured 

 alike, but are less asymmetrical than usual in that 



