154 



Descriptive Zoology. 



Some appear to live permanently in our large lakes. By 

 their sucking mouths they attach themselves to fishes, 



FIG. 99. LAMPREY EEL. 



After Goode. From Kingsley's Zoology. 



sucking their blood, or even penetrating their bodies. 

 They are the only vertebrates known to live a parasitic 

 life. In Europe the sea lampreys are valued as food. 



CLASS PISCES. 

 Example. The Ringed Perch. 



Life of a Perch. If one stops to consider what are the 

 chief objects in life with a fish, he soon sees that it is well 

 expressed in the words "to eat and not be eaten." 



FIG. ioo. EXTERNAL FEATURES OF A PERCH. 



In order to secure food and escape enemies the fish 

 must have sense organs and organs of locomotion. 



