THE FISH. 



PERCH, SUCKER, GUNNER, OR OTHER BONY FISH. 



WHILE the following directions have been made with 

 reference to the perch, the others named, or indeed almost 

 any species at hand may be employed. It will be especially 

 valuable to have a few living specimens, minnows or gold- 

 fish, in a laboratory aquarium for actual observations of 

 movements. 



For dissection preserved specimens are quite as good as 

 those freshly killed or obtained from the market; the last 

 are likely to have been kept in storage for some time and 

 the internal organs are often worthless for study.* 



I. General Features. 



Note the shape of the body and its special differential 

 features head, tail, body proper, fins. Are the body 

 features sharply marked? How do they compare with 

 those of the frog? Is the shape adapted to the life and 

 habits of the fish? Note the scales, their shape and arrange- 

 ment. Are they found on all parts of the body? How are 

 they attached to the body? What is their relation to the 

 skin? Examine a few quite critically and decide whether 

 they are entirely naked and whether the margin is smooth 

 or toothed. A scale with a smooth, rounded outline is 

 called cycloid, one with a toothed margin is called ctenoid; 

 to which of these does your specimen belong? 



