20 



fauna is a remarkable mixture of fresh-water fishes from the 

 Mississippi and marine fishes from the Gulf. Channel-cats, 

 sharks, sea-crabs, sunfishes, and mullets can -all be found there 

 together. It is therefore to be expected that the lowland fauna 

 of all the rivers of the Gulf States would closely resemble that 

 of the lower Mississippi ; and this, in fact, is the case. 



The low and irregular water-shed which separates the tribu- 

 taries of Lake Michigan and Lake Erie from those of the Ohio 

 is of little importance in determining the range of species. 

 Many of the distinctively Northern fishes are found in the head- 

 waters of the Wabash and the Scioto. The considerable dif- 

 ference in the general fauna of the Ohio Valley as compared 

 with that of the streams of Michigan is due to the higher 

 temperature of the former region, rather than to any existing 

 barriers between the river and the Great Lakes. In northern 

 Indiana the water-shed is often swampy, and in many places 

 large ponds exist in the early spring. 



At times of heavy rains many species will move through 

 considerable distances by means of temporary ponds and 

 brooks. Fishes that have thus emigrated often reach places 

 ordinarily inaccessible, and people finding them in such locali- 

 ties often imagine that they have "rained down." Once, near 

 Indianapolis, after a heavy shower, I found in a furrow in a 

 corn-field a small pike [Esox vermiciilatiLS Le Sueur), some 

 half a mile from the creek in which he should belong. The fish 

 was swimming along in a temporary brook, apparently wholly 

 unconscious that he was not in his native stream. Migratory 

 fishes, which ascend small streams to spawn, are especially 

 likely to be transferred in this way. By some such means 

 any of the water-sheds in Ohio, Indiana, or Illinois may be 

 passed. 



It is certain that the limits of Lake Erie and Lake Michigan 

 were once more extended than now. It is reasonably probable 

 that some of the territory now drained by the Wabash and the 

 Illinois was once covered by the waters of Lake Michigan. 

 The Cisco {Coregomis artedi sisco Jordan), of Lake Tippecanoe, 

 Lake Geneva, and the lakes of the Oconomowoc chain, is evi- 

 dently a modified ' descendant of the so-called lake herring 



