CHAPTER XVI. 
THE STRUCTURE AND ACTIVITIES OF A FISH. 
GOLDFISH or other small fish from streams or 
ponds are easily kept in aquaria. With a few living 
fish placed where pupils can observe them, and a 
smelt or perch from the market as an individual 
specimen for study on each bench, the following ques- 
tions may be answered: 
Shape and Covering, Is the fish bilateral? Esti- 
mate length, thickness, and depth. 
What is the shape of the body ? 
Do you find a head? a neck? 
Do you find scales? Do they cover the entire 
animal ? 
Are the scales joined edge to edge (¢esselated) or 
do they overlap (¢méricated)? 
Remove some of the skin. What is the appearance 
of the muscle below ? 
Notice the line extending along the side of the fish 
from head to tail (/a¢eral line). Do the scales cover- 
ing this line differ from those found elsewhere on the 
body? 
The Fins. How many fins do you find? How 
many are dorsal? How many ventral? How many 
are paired ? 
Which fins correspond to the limbs on our own 
bodies ? 
The paired fins nearest the head of the perch are 
_called the pectoral fins, those somewhat farther back 
nearer the anal opening are called the pelvic fins. The 
large fin along the back is the dorsal fin. The unpaired 
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