DISPERSION OF FRESH-WATER FISHES. gI 
seck the highest streamlets in the mountains; but 
except to call attention to the cavernous character 
of the Subcarboniferous and Devonian limestones, 
Professor Cope has made little attempt to account 
for it. 
Professor Cope finally concludes with this im- 
portant generalization: — 
“It would appear, from the previous considerations, 
that the distribution of fresh-water fishes is governed by 
laws similar to those controlling terrestrial vertebrates and 
other animals, in spite of the seemingly confined nature of 
their habitat.” 
Dr. Giinther! has well summarized some of the 
known facts in regard to the manner of dispersion 
of fishes : — 
“The ways in which the dispersal of fresh-water fishes 
has been effected were various. They are probably all 
still in operation, but most work so slowly and imper- 
ceptibly as to escape direct observation; perhaps they 
will be more conspicuous after science and scientific 
inquiry shall have reached a somewhat greater age. 
From the great number of fresh-water forms which we 
see at this present day acclimatized in, gradually accli- 
matizing themselves in, or periodically or sporadically mi- 
grating into, the sea, we must conclude that under certain 
circumstances salt water may cease to be a barrier at 
some period of the existence of fresh-water species, and 
that many of them have passed from one river through 
salt water into another. Secondly, the head-waters of 
some of the grandest rivers, the mouths of which are at 
opposite ends of the continents which they drain, are 
sometimes distant from each other a few miles only. The 
1 Guide to the Study of Fishes, 1880, p. 211. 
