360 MANUAL OF ZOOLOGY. 



the water required in respiration is taken in at the mouth by a 

 process analogous to swallowing. 



VI. The nasal sacs never communicate posteriorly with the 

 cavity of the pharynx. 



The subdivisions of the osseous fishes are so numerous, and 

 they contain so many families, that it will be sufficient to run 

 over the more important sub-orders, and to mention the more 

 familiar examples of each. 



SUB-ORDER A. MALACOPTERI, Owen (= Physostomata, Miil- 

 ler). This sub-order is defined by usually possessing a com- 

 plete set of fins, supported by rays, all of which are " soft " or 

 many-jointed, with the occasional exception of the first rays in 

 the dorsal and pectoral fins. A swim-bladder is always present, 

 and always communicates with the oesophagus by means of a 

 duct, which is the homologue of the windpipe. The skin is 

 rarely naked, and is mostly furnished with cycloid scales ; but 

 in some cases ganoid plates are present. 



This sub-order is one of great importance, as comprising 

 many well-known and useful fishes. It is divided into two 

 groups, according as ventral fins are present or not. In the 

 first group Apoda there are no ventral fins ; and the most 

 familiar examples are the common Eels of our ' own country. 

 More remarkable, however, than the ordinary Eels is the 

 Gymnotus elcctricus, or great Electric Eel, which inhabits the 

 marshy waters of those wonderful South American plains, the 

 so-called " Llanos." This extraordinary fish (fig. 13.5) is from 



Fig. 135. Electric Eel (Gymnotus electricus). 



five to six feet in length, and the discharge of its electrical 

 organs is sufficiently powerful to kill even large animals. The 

 following striking account is given by Humboldt of the manner 

 in which the Gymnoti are captured by the Indians : " A 

 number of horses and mules are driven into a swamp which is 

 closely surrounded by Indians, until the unusual disturbance 

 excites the daring fish to venture an attack. Serpent-like, 



