XIII 



PHYLUM CllUllDATA 



227 



Many Shore-fishes exhibit protective characters, the tints and 

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

 sea-weeds, &c., among wiiich 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 

 eye rather crude and glaring, they appear to be distinctly protec- 

 tive, harmonising with the brilliant hues of the Coral Polypes 



Fig. SS2.— Pleuronectes cynoglossus (Craig-fluke), from the right side. d. j. dorsal fin ; 



I. e. left eye ; yd. f. pectoral fin ; xj<-'- f. pelvic fin ; r. e. right eye ; c. /. ventral fin. (After 

 Cuvier.) 



and other members of the reef fauna. Pelagic fishes, such as the 

 Mackerel and Herring, are usually steely-blue above, white 

 beneath. 



Many deep-sea Teleostei are phosphorescent : in some of these 

 definite luminous organs (Fig. 883) are arranged in longitudinal 

 rows along the body, each provided with a lens and other accessory 

 parts, like those of the eye, the whole organ having the character 

 of a minute bull's-eye lantern. Some species of the same order, 

 such as the Weaver {Trachinus), possess poison- glands, opening 

 either on one of the dorsal spines, or on a spinous process of 

 the operculum, or, as in the Cat-fishes (Siluridse), on the spine 

 of the pectoral fin. 



Exoskeleton. — In many Teleostomi, such as Polyodon and 

 the Eels, the skin is devoid of hard parts, but in most cases a 



