THE FLOUNDER. 
171 
Holotliurians, etc. F. aciis lives in Holothurians, and 
another species in a sfcar-flsli. 
At the head of the Tdeocepliali stand the flounders, hali- 
but, and solos, Avhich 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^ 
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.^., when the flounder {Plagusia) is twenty-five milli- 
metres (one inch) .ong. 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- 
FiG. 217.— Goose-fish, one tenth natural size. 
