FISHES 216 



look after its eggs. The young fish live upon crustaceans 

 and small worms, but, in turn, may be eaten by larger fish. 

 Some fish scoop rude nests out in the gravel in which to 

 deposit their eggs and then stand guard over them to pro- 

 tect them. The stickleback builds quite an elaborate nest 

 for its eggs and the male assiduously cares for them. 



Other Ex.-vmples of this Class 



Sharks, rays, sawfish, etc. — These examples are repre- 

 sentatives of the lowest order of fishes. The sharks are 



Fig. 151. — Hammer-headed shark. Note the five gill slits in the side 

 of the neck. 



the lowest in development of the fishes. At the same time, 

 they are the fiercest animals of the sea. 



In some sharks the body is protected by spiny processes, 

 and in others the body has no protection at all ; but very 

 few animals dare to attack them. In general, the skeleton 

 is cartilaginous, with no distinct bones as in the higher 



