PISCES. 207 



are highly prized by some nations. The love borne them by the ancient 

 Romans is a matter of classical history, and at the present day they are 

 favorite food of epicures. A prominent European species is the Petro- 

 myzon ßuviatilis, shown in;?/. 81, ßg. 28. The Petroimjzon americaiius is 

 the largest and best known American species. The genus Ammoccetes, 

 with the general characters of the lampreys, differs mainly in the form of 

 the mouth. This, instead of being continuous and suctorial, is composed of 

 a circular projecting upper lip, the lower being transverse. The opening 

 of the throat is guarded by a fringe of cili«. This genus is extensively 

 distributed over North America, where several species are known. They 

 accumulate in vast numbers in certain sand or mud flats, as those of the 

 Susquehanna river, whence they are dug from a depth of four or five 

 inches below the level of the water, to serve as bait for other fishes. 



The SYMBRANCHiDiE are anguilliform fishes, distinguished from their 

 allies by the greater or less union of both branchial apertures into one. 

 The fins also are variously suppressed, some being without pectorals, and 

 others without either these or vertical fins. The next family. 



The MuR^NiD^ or eels, with the normal structure of the gill aper- 

 tures, yet have them very small and capable of being completely closed. 

 The body is serpentiform, and although provided with scales, these are 

 scarcely apparent, being embedded in a thick mucous skin. The air- 

 bladder is polymorphous, and the intestines without coeca. The eels, in 

 their different species, are inhabitants of both fresh and salt waters ; those 

 living; in the former belonging generally to the restricted genus Anguilla. 

 Species of Anguilla occur in greater or less number throughout the United 

 States, being, however, very rare in many if not most of the waters of the 

 Mississippi basin. Popular opinion assigns to these species a viviparous 

 reproduction, owing to the apparent absence of individuals containing eggs. 

 The ova are yet, probably, present in a due proportion of the supposed 

 males, escaping observation by their diminutive size. The eel hardly yields 

 to any other fish in the power of sustaining a deprivation of its proper 

 element for a considerable length of time. To transport these animals over 

 a considerable space, all that is necessary is to pack them in damp grass or 

 some similar substance. They even leave the water spontaneously at 

 night in search of food, or of a body of water better suited to their conve- 

 nience than the one in which they may happen to be placed. Eels are 

 said to be very susceptible to magnetic or galvanic influence : the simple 

 contact of a knife being sufficient to paralyse them. When a magnet is 

 presented to the dish in which the living animal may happen to be, violent 

 contortions, a painful gasping after breath, and other signs of inconvenience, 

 are reported to be exhibited. PI. 82, fig. 5, is a figure of Anguilla vulgaris. 



The Gymnotid^, highly interesting on account of their electrical proper- 

 ties, are characterized by the anterior position of the anus, the entire 

 absence of dorsal fin, the extent of the anal, and the position of the gill- 

 opening. The best known species, Gymnotus eleclricus or electric eel, is a 

 native of the tropical portions of South America. It attains to a great 

 size, being sometimes over six feet in length, and almost a full load for a 



411 



