CHAPTER X 



PISHES 



103. Vertebrates. — All of the animals thus far studied 

 are grouped together under the name of Invertebrate*. 

 because they have no backbone. We are now to study 

 the Vertebrates, animals with a backbone, such as fishes, 

 frogs, snakes, and birds. 



The presence of a backbone in vertebrates is their most 

 conspicuous characteristic. The formation of the back- 

 bone is always preceded by the growth of an embryonic 



Figure 104. — Skeleton of Fish. 

 Note backbone. 



group of cells that do the work of a skeleton. This 

 embryonic group of cells forms a structure which is called 

 the notocliord (no'to-kord : Greek, notos, back; chorda, 

 cord). In all of the true vertebrates (such as fishes, 

 frogs, etc.), the notochord is gradually absorbed and the 

 backbone takes its place, but between the vertebrae it 

 remains as cushions. But in the fish-like animal railed 



103 



