FISHES. 125 



membranes which are easily torn ; they serve the same purpose as the columns in the 

 analogous organ of the torpedo, making the walls or abutments for the perpendicular 

 and transverse dissepiments, which are exceedingly numerous and so closely aggre- 

 gated as to seem almost in contact. The minute prismatic cells, intercepted between 

 these two sorts of plates, contain a gelatinous matter ; the septa are about one-thirtieth 

 of an inch from each other, and one inch in length contains a series of two liundred 

 and forty cells, giving an enormous surface to the electric organs. The whole appara^ 

 tus is supplied by more than two hundred nerves, which are the continuation of the 

 rami anteriores of the spinal nerves. In their course they give out branches to the 

 muscles of the back, and to the skin of the animal. In the electi-ic eel, as in the tor- 

 pedo, the nerves supplying the electric organs are much larger than those bestowed on 

 any part for the purposes of sensation or movement." (^Gilnther.) . 



The Stbrnopygid^ are smaller in size, and the body is covered with small scales, 

 and not provided with an electric organ. The species abound in the j-ivers of tropical 

 South America ; about twenty are recorded. 



SiTB-OeDBR II. — EVENTOGNATHI. 



The sub-order of Eventognathi or Plectospondyli comprises a vast assemblage of 

 fresh-water fishes, some of which are found in almost all parts of the globe. They 

 are physostomous fishes, with the anterior vertebrae united and modified as in the 

 Nematognathi and the Gymnonoti, but without most of the other peculiarities of these 

 groups. Professor Cope thus defines the group, which he calls Plectospondyli : " Pari- 

 etals broad, distinct; pterotic normal, symj)lectic present; opercular bones all present; 

 no interclavicles ; anterior four vertebrae much modified, and with ossicula auditus." 

 The name Plectospondyli alludes of course to the union of the anterior vertebrae. The 

 name Eventognathi, of earlier date, refers to the peculiar development of the lower 

 pharyngeal bones which is found in many of the fishes of this order, — in all which 

 inhabit the north temperate zone. This structure will be described farther on. Those 

 not having falciform pharyngeals (Characinidse) have been placed among the Isospon- 

 dyli by Dr. Gill, but they probably belong rather with the present group, although in 

 many regards they resemble the Salmonoid fishes. 



The Eventognathi may be divided into six families. Of these, the Characinidse 

 have the lower pharyngeals not falciform, the jaws usually with teeth, the gill open- 

 ings various, and an adipose fin usually developed. The others all agree in having 

 the lower jjharyngeals more or less falciform and parallel with the gill arches, the 

 mouth toothless, the gill openings restricted to the sides, and no adipose fin. In both 

 groups, so far as I know, there are but three branchiostegals. 



The family KNEEiiDiE is composed of two little minnow-like fishes belonging to 

 the genus Kneria, and inhabiting the streams of central Africa. They differ from the 

 Cyprinidae mainly in the entire absence of pharyngeal teeth. 



The HoMALOPTERiD^ comprise about thirteen species of small loach-like fishes, 

 inhabiting the mountain streams of the East Indies. They have no air-bladder, and 

 the number of phai-yngeal teeth is greater than that seen in the loaches or carp, being 

 from ten to sixteen. 



The CoBiTiD^, or loaches, are small fishes, all less than a foot in length, inhabiting 

 the fresh waters of Europe and Asia. They are allied to the minnows in structure, 

 but are for the most part slender and somewhat eel-like in form. The mouth is sur- 



