FISHES 



119 



front of the optic lobes lie the two cerebral lobes, or the cerebrum. 

 The small olfactory lobes are seen (Fig. 224) in front of the cere- 

 brum. The olfactory nerves may be traced to the nostrils. Back 

 of the optic lobes (mid brain) is the cerebellum (hind brain), and 



back of it is the medulla oblongata, 

 or beginning of the spinal cord. 



FIG. 223. BRAIN OF PERCH, 

 side view. 



FIG. 224. BRAIN OF PERCH, 

 from above. 



Taking the eyeball for comparison, is the whole brain as large 

 as one eyeball? (Fig. 222.) Judging from the size of the parts of 

 the brain, which is more important with the fish, thinking or per- 

 ception? Which is the most important sense? 



The scales along a certain line on each side of the fish, called 

 the lateral line, are perforated over a series of lateral line sense 

 organs, supposed to be the chief organs of touch (see Fig. 209). 



Questions. Which of the fins of the fish have a use 

 which corresponds to the keel of a boat ? The rudder ? A 



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FlG. 225. THE STICKLEBACK. Instead of depositing the eggs on 

 the bottom, it makes a nest of water plants the only fish that does 

 so and bravely defends it. 



