72 
FISHES 
fish ends in a large median fin. The tail region is chiefly 
important in locomotion, but the fins also help in balancing 
and steering. 
Scales cover the trunk and tail, each one overlapping like 
the shingles of a house. The skin is full of mucous glands 
that keep the fish covered with slime. Both the slime and 
the scales protect the fish (Figure 63). 
LABORATORY STUDY 
Study living fish, such as goldfish or perch. Place one or two in an 
aquarium and observe their behavior. Fill out the report below. 
Number 
Number of 
Paired 
Fins 
Number of 
Unpaired 
Fins 
Which are Used to 
Do THE 
Eyes 
Move ? 
of Fins 
Advance ? 
Stop ? 
Balance ? 
Note the shape and relative position of the head, trunk, and tail 
region. The gills are covered by a bony shield, the operculum. What 
is its size and how attached? Where are the eyes located? Do they 
move? Can the eyes be closed? How is the body covered? Of 
what use is this covering to the fish? 
57. Locomotion. — The bodies of such fishes as are shown 
in Figures 59-61 are adapted to swimming. The tapering 
head offers but little resistance to the water and the general 
spindle-shape of the whole body enables it to move easily 
when completely surrounded by water. Notwithstanding 
that there are paired fins which are similarly placed to the 
paired legs of a frog or dog, these fins are not important in 
giving speed to the fish’s movements. They act as brakes 
when the fish desires to stop, the brake being applied by 
simply straightening out these paired fins at right angles 
to the body. The median fins on the back and lower sur- 
