VERTEBRATES 105 



attached to the skin. In what way is the lateral-line scale 

 specialized ? 



7. State how, when the fish is swimming, the nostrils 

 catch odors. By means of a diagram, with arrows show 

 the probable direction of the water current through the 

 nose. 



8. State which of the structures of your eye are present 

 in the fish's eye, and which are missing. Could a fish 

 weep ? wink ? How would a fish sleep .-' 



9. Inasmuch as light penetrates water but a little way, so that 

 objects can be distinguished only within about thirty feet, would the 

 fish be nearsighted or farsighted ? 



Suggested drawings. 



a. A side view of the entire fish, fully labeled. 



b. A bony rayed and a cartilaginous rayed fin. 



c. A scale, showing its minute structure. 



d. A dorsal or a lateral view of the head, showing the 

 sense organs. 



The Mouth and the Gills of^the Fish 

 Materials. 



T)ie same materials as those used in the preceding 

 exercise may be used here. 



Directions. 



The mouth, its structure and its action, can be seen by 

 pulling the upper jaw upward and forward until the mouth 

 and the gill chambers open fully. Examine the structure 

 and action of the jaws, the tongue, the throat, and the 

 teeth on each jaw and on the roof of the mouth. 



Investigate the breathing apparatus from the throat side 

 and from the exterior, noting the number, form, and struc- 

 ture of the gills, their attachment and their protection. 



