17 



BACKBONED -ANIMALS. 



that dry up, and crawl overland (see frontispiece) in great 

 numbers in search of water, during this time breathing air 

 directly. The Arges are almost blind forms, living in sub- 

 terranean streams. A cat-fish from the Nile, Malapterus 

 electricus (Fig. 209), is electric, the cells forming a layer 

 over the entire body except the head and fins. The South 

 American Lau-Lau, is the largest of the family, and pro- 

 tects its young in its mouth. The Corbetis fossilis (Fig. 2 10^ 



FIG. 210. Corbetis fossilis. It swallows air-bubbles which pass through the 

 intestine, where the mucous membrane takes up the oxygen for respiration. 



breathes air directly as well as taking it from the water. 



The fourth order- of fishes, Scyphophori, is represented by 



the Nile Gymnarchus. 



Order V. Perfect-headed Fishes (Teleocephali). 



General Characteristics. This order embraces most of our 



common fishes. 

 The skeleton is 

 bony, and the 

 name applies 

 to the diversity 

 and perfection 

 of the bones of 

 the head. 



Gymnotus. 

 The Gymno- 



FIG. 2ii. Electric eel {Gymnotus electricus]. 



tus electricus 

 (Fig. 211) is 

 one of the lowest of the Teleosts. The batteries are 

 four in number, and situated, in pairs, on each side of 

 the body, occupying together nearly all the lower portion. 



