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 fluviatilis, shown in pl. 81, fig. 28. The Petromyzon americanus is 
the largest and best known American species. The genus Ammocetes, 
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 cilia. 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 Symprancnip# 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 Muranip# 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 ceca. 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. PJ. 82, fig. 5, is a figure of Anguilla vulgaris. 
The Gymnotip&, 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 electricus 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 
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