CLASS PISCES 449 



give brown. Usually the colors are arranged in a definite 

 pattern consisting of transverse or longitudinal stripes, and 

 spots of various sizes. Coral-reef fishes have long been famous 

 for their brilliant colors, and many fresh-water fishes of the 

 temperate zone exhibit bright hues distributed so as to form 

 striking and intricate patterns (e.g. the rainbow darter). 



The contraction and expansion of the chromatophores of 

 certain fishes result in changes in coloration. These changes 

 " are due to incident light reflected from surrounding surfaces, 

 acting through the visual organs and the nervous system on the 

 differently colored chromatophores." (Bridge.) The changes 

 are therefore dependent upon the color of the fish's environment, 

 and are often such as to conceal the animal, being consequently 

 protective. The change is slow in many fishes, but may be 

 quite rapid, as in the flounder. Male fishes are often more 

 brightly colored than the females, especially during spawning 

 activities. 



The Skeleton. - - The skeleton differs among the fishes chiefly 

 in the relative amount of bone and cartilage. Both the TELEO- 

 STOMI and DIPNOI possess skeletons which consist to a greater 

 or less extent of bones preformed in cartilage, and membrane 

 bones which are developed as dermal ossifications. The ver- 

 tebra are usually amphiccelous, as in the perch, and bear neural 

 arches; some of them in the trunk region bear ribs; others in 

 the tail bear haemal arches. There is no sternum. 



The cranium is independent of the visceral arches. It is 

 complicated in the teleosts by the addition of numerous mem- 

 brane bones. The visceral skeleton consists of seven arches ; five 

 of them are usually gill-arches. The lower jaw articulates with 

 the upper jaw and not directly with the cranium. The bones 

 contained in the gill-cover or operculum develop from the hyoid 

 arch. 



The Digestive System. - - The food of our common fishes 

 consists of vegetation, insect larvae, crustaceans, mollusks, and 

 other smaller fishes. Some fishes are voraciously carnivorous, 



2G 



