xiii PHYLUM CHORDATA 211 



thoracic, or on the throat (Fig. 828), when they are said to be 

 jugular in position. 



A very remarkable deviation from the typical form occurs in the 

 Flat-fishes (^Pleuronectidce) , a family of Anacarithini. The body 

 (Fig. 833) is very deep and strongly compressed : the fish habitually 

 rests on the bottom, in some species on the right, in others on the 

 left side, partly covering itself with sand, and occasionally swim 

 ming with a curious undulating movement. The under side is 

 usually pure white, the upper side dark. The eyes (r.e, I.e.) are both 

 -on the upper or dark-coloured side, and the skull is distorted so as 

 to adapt the orbits to this change of position. The abdominal 

 cavity is very small, the vent placed far forward, and the dorsal 



FIG. 833. Pleuronectes cynoglossus (Craig-fluke), from the right side. d. f. dorsal fin ; 

 /. (. left eye ; pct.f. pectoral fin ; pr.j. pelvic fin ; r. e. right eye ; r./. ventral fin. (After 

 Cuvier.) 



and ventral fins are continuous. Young Flat-fishes swim in the ordi- 

 nary vertical position, but after a time they lie on one side and 

 assume the adult peculiarities, the eye on the lower side gradually 

 rotating until it reaches the upper surface. 



Many Shore-fishes exhibit protective characters, the tints and 

 markings of the skin being harmonised with those of the rocks, 

 sea-weeds, &c., among which they live. The effect may be 

 heightened by fringes and lobes of skin, resembling sea-weed, and 

 often giving the fish a most grotesque appearance. The colours 

 are often adaptable : Trout, for instance, alter their colour by the 

 contraction or expansion of their pigment-cells, according to 

 whether the streams in which they live have a muddy or a sandy 

 bottom. In some Shore-fishes, such as those of the coral reefs 

 the colours are of the most brilliant description : vivid reds, blues, 

 and yellows, spots or stripes of gold or silver, are common, and, 

 although the combination of tints may sometimes seem to our 



p 2 



