TEE FLOUNDER. 



171 



Holotliurians, etc. F. acus lives in Holothurians, and 

 another species in a star-fisli. 



At the head of the Teleocephali stand the flounders, hali- 

 Dut, and soles, which are an extremely modified type of the 

 order. In these fishes the body is very unsymmetrical, the 

 fish virtually swimming on one side, the eyes being on 

 the upper side of the head. The upper side is colored 

 dark, due as in other fishes to pigment-cells; the lower side 

 IS colorless, the pigment-cells being undeveloped. When 

 first hatched the body of the flounder is symmetrical, and m 

 form is somewhat cylindrical, like the young of other fishes. 



Fig. si?.— Goose-flsh, one tenth natural size. 



swimming vertically as they do, and with pigment-cells on 

 the under side of the body. The flounder is not born with 

 the eyes on the same side of the head, but one eye gradu- 

 ally passes from the blind to the colored side; the transfer 

 of the eye from the blind side to the colored side occurs 

 very early in life, while all the facial bones of the skull are 

 still cartilaginous, long before they become hard and ossi- 

 fied, i.e., when the fiounder (Plagusia) is twenty-five milli- 

 metres (one inch) lOng. Young flounders, when less than 

 two inches in length, are remarkably active compared 

 with the adults, darting rapidly through the water after 

 their food, which consists principally of larval surface- 



