Pisces. 69 



in the structure of the two. Why should the darters have this 

 habit of staying on the bottom ? 



Senses of Fishes. Watch the movements of the eyes of a fish. 

 What range of movement have they? Do the eyes move simulta- 

 neously? Does a fish see any better than you do? Devise means 

 of testing the sense of hearing without affecting the other senses. 

 Test the different senses in various ways. On which senses does 

 the fish most rely for safety ? 



Food and Mode of Eating. Offer a fish various kinds of food and 

 find what it likes best. How does it take its food ? What relation 

 has the shape or size of the mouth to the kind of food taken? 

 Does a fish eat much, or little, relatively? In feeding fishes take 

 care not to give too much at one time, for fear of fouling the water. 

 Do fishes suffer from overeating? 



Sleep. Do fishes sleep? Have they any special resting place 

 or resting position ? 



EXTERNAL FEATURES OF A FISH. 



For this work, and the dissection that follows, the perch is pref- 

 erable for inland students, though the bass, croppie, or sunfish 

 serves very well. On the seacoast the cunner or the sea perch 

 is more accessible. 



Lay the fish on a sheet of thick paper, on a plate, or in the dis- 

 secting pan. 



i. Notice the shape of the fish as a whole ; how is it adapted for 

 motion through the water? Hold the fish with the back uppermost 

 and the head directly away from you ; instead of speaking of the front 

 and hind ends, it is better to call them the anterior and posterior 

 ends. The upper surface, or back, is the dorsal surface, and the 

 lower the ventral surface. The right and left sides are counter- 

 parts of each other ; that is, the fish is bilaterally symmetrical. 



The perch is flattened from side to side, and is therefore said to 

 be compressed. A fish is properly described as " flat " only when 

 flattened on the dorsal and ventral surfaces, or depressed, as in the 

 case of the rays. 



