228 FOOT-NOTES TO EVOLUTION. 
The coral reef is the metropolis of the fish. The 
deep sea, the arctic sea, and the isolated rivers—these 
are the ichthyological backwoods. 
An exception to the general rule in regard to the 
numbers of vertebre is found in the case of the eel. 
Eels inhabit nearly all seas, and every- 
where they have many vertebre. The 
eels of the tropics are at once more specialized and more 
degraded. They are better eels than those of northern 
regions, but, as the eel is a degraded type, they have 
gone further in the loss of structures in which this de- 
generation consists. 
It is not well to push this analogy too far, but per- 
haps we can find in the comparison of the tropics and 
the cities some suggestion as to the development of 
the eel. 
In the city there is always a class which follows in 
no degree the general line of development. Its mem- 
bers are specialized in a wholly different way. By this 
means they take to themselves a field which others have 
neglected, making up in low cunning what they lack in 
humanity or intelligence. 
Thus, among the fishes, we have in the regions of 
closest competition this degenerate and non-fishlike 
type, lurking in holes among the rocks, or creeping in 
the sand; thieves and scavengers among fishes. The 
eels thus fill a place otherwise left unfilled. In their 
way they are perfectly adapted to the lives they lead. 
A multiplicity of vertebral joints is useless to the typical 
fish, but to the eel, strength and suppleness are every- 
thing. No armature of fin or scale or bone is so de- 
sirable as its power of escaping through the smallest 
opening. 
Origin of eels. 
