112 



BEGINNERS' ZOOLOGY 



the fish immovable, slightly movable, or freely movable? 



Can it look with both eyes at the same object? Is the 



range of vision more upward or downward ? To the front 



or the side? In 

 what direction is 

 vision impossible? 

 Can a fish close its 

 eyes i u sleep ? Does 

 the eyeball appear 

 spherical or flat- 

 tened in front ? 

 Fig. 210. — Blackboard Outline of Fish. The ball is really 



spherical, the lens is very convex, and fish are nearsighted. 



Far sight would be useless in a dense medium like water. 



In what direction from the eyes are the nostrils (Fig. 



211.) There are two pair of nostrils, but there is only one 



pair of nasal cavities, with two nostrils opening into each. 



There are no nasal passages to . 



the mouth, as the test with a 



probe shows that the cavities do 



not open into the mouth. What 



two functions has the nose in man? 



What function has it in the fish? 



Fig. 2ii. — Head of Carp. 



There are no external ears. 

 The ear sacs are embedded in the 

 bones of the skull. Is hearing acute or dull? When you are 

 fishing, is it more necessary not to talk or to step lightly, 

 so as not to jar the boat or bank ? 



What is the use of the large openings found at the back 

 of the head on each side ? (Fig. 211.) Under the skin at 

 the sides of the head are thin membrane bones formed from 

 the skin ; they aid the skin in protection. Just under these 

 membrane bones are the gill covers, of true bone. Which 



