TYPICAL FAMILIES OF THE APODES. 219 



tiles : and when we consider that some of the foreign 

 eels have actually no fins whatever, the only essential 

 difference that remains between them and serpents is 

 their diverse modes of respiration. This theory^ again, 

 receives strong support, if not direct confirmation, by 

 the structure of the branchia in Petromyson, which is 

 precisely that of the cartilaginous fishes ; it thus effects 

 the union of that order with the Apodes, so that the 

 three aberrant divisions of the whole class become united 

 into one circle : there is, in short, no other mode of ac- 

 counting for this singular departure of Petromyzon from 

 Myooejie and Gastrobranchus,— two genera with which, in 

 all other respects, it is so naturally and confessedly allied. 

 Viewed in this light, the apparent anomaly becomes abso- 

 lute harmony ; since, were the branchia of the lampreys 

 like those of the Myxene, no passage whatever could be 

 traced between the Apodes and the Cartilagines. 



(19-^.) Without entering, in this place, into sci- 

 entific details, or lengthened popular descriptions, we 

 may yet make a few general observations on the dif- 

 erent families under which, for the first time^ we have 

 distributed the genera. The typical families, MurcB- 

 nidw and Synbranchid<s, comprise all the true eel- 

 shaped fishes, having serpent-like bodies, long and 

 cylindrical : they are either naked, or with scales so 

 minute as to be barely perceptible. In the first, 

 the branchial spiracle, or opening, is situated as in the 

 generality of fishes, that is, on the sides of the neck, 

 close to the pectoral fin {fig. 38. a) ; but, in the latter 

 family, they are always placed on the under part of 

 the throat, and thus are close together. Their general 

 aspect is so like that of reptiles, that they may be termed 

 serpent-eels, in contradistinction to the former, or true 

 eels. The habits of the Murcenida:, in general, are pretty 

 much the same as those of the common eel and the 

 conger. Some few are confined to fresh waters, but the 

 majority live near the mouths of rivers. The eels, pro- 

 perly so called, have pectoral fins ; but in the MurcBncB, 

 or sea eels^ no pectorals exist, as in Gymnothoraoo Zebra 



