170 BACKBONED ANIMALS. 
that dry up, and crawl overland (see frontispiece) in great 
numbers in search of water, during this time breathing air 
directly. The Azges 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 Zau-Lau, is the largest of the family, and pro- 
tects its young in its mouth. The Corbetis fossilis (Fig. 210! 
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 ( 7¢leocephaii).— 
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. 
Gymunotus. 
—The Gymno- 
tus electricus 
(Fig. 211) is 
one of the lowest of the TZeleosts. The batteries are 
four in number, and situated, in pairs, on each side of 
the body, occupying together nearly all the lower portion. 
