494 



TELEOSTEI 



[CH. 



pelvic fins moved forward into a jugular position. For this reason 

 they were formerly placed near to the Cod family, but Tate Regan 

 has shown that they must be regarded as having sprung from the 

 Percomorphi. One primitive genus, Psettodes, still possesses spines 

 the dorsal fin. The Heterosomata derive their name from the fact 

 that they habitually lie on one side, which is usually white, whilst 

 both eyes are twisted on to the upper side which is deeply pig- 

 mented. The air-bladder is lost. These fish, which are captured 

 by the trawl net which is dragged over the bottom, include a large 

 proportion of our most valued food-fish such as the Plaice (Pleuro- 

 nectes platessa) (Fig. 241), the Flounder (P. flesus), the Dab (P. 



FIG. 241. Pleuronectes platessa, the Plaice, found from the coast of France to 



Iceland. 



limander), the Lemon Sole (Glyptocephalus microcephalus\ the 

 Turbot (Psetta maxima), the Brill (Psetta laevus), the Sole (Solea 

 vulgaris] and the Halibut (Hippoglossus), which may 'attain a length 

 of 10 feet and weigh 400 Ibs. 



As everyone knows, the Sole is one of the most valued fish, and 

 appears chiefly at the tables of the rich, whilst the Plaice is the food 

 of poorer people. 



The reason for this is curious : all fistrowe their palatability to 

 some peculiar chemical substance in the muscles which gives them 

 their characteristic flavour. In the Plaice, as in most fish, the 

 substance is present in the fish when living, and consequently unless 



